diff --git a/README.md b/README.md
index e673184..bbe0010 100644
--- a/README.md
+++ b/README.md
@@ -53,10 +53,10 @@ Language](https://doc.rust-lang.org/book/second-edition/ch03-02-data-types.html)
 
 - ["primitive_types1.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types1.rs%0A%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Booleans+%28%60bool%60%29%0A%0A++++let+is_morning+%3D+true%3B%0A++++if+is_morning+%7B%0A++++++++println%21%28%22Good+morning%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+the+rest+of+this+line+like+the+example%21+Or+make+it+be+false%21%0A++++if+is_evening+%7B%0A++++++++println%21%28%22Good+evening%21%22%29%3B%0A++++%7D%0A%7D%0A)
 - ["primitive_types2.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types2.rs%0A%2F%2F+Fill+in+the+rest+of+the+line+that+has+code+missing%21%0A%2F%2F+No+hints%2C+there%27s+no+tricks%2C+just+get+used+to+typing+these+%3A%29%0A%0Afn+main%28%29+%7B%0A++++%2F%2F+Characters+%28%60char%60%29%0A%0A++++let+my_first_initial+%3D+%27C%27%3B%0A++++if+my_first_initial.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+my_first_initial.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%0A++++let+%2F%2F+Finish+this+line+like+the+example%21+What%27s+your+favorite+character%3F%0A++++%2F%2F+Try+a+letter%2C+try+a+number%2C+try+a+special+character%2C+try+a+character%0A++++%2F%2F+from+a+different+language+than+your+own%2C+try+an+emoji%21%0A++++if+your_character.is_alphabetic%28%29+%7B%0A++++++++println%21%28%22Alphabetical%21%22%29%3B%0A++++%7D+else+if+your_character.is_numeric%28%29+%7B%0A++++++++println%21%28%22Numerical%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Neither+alphabetic+nor+numeric%21%22%29%3B%0A++++%7D%0A%7D%0A)
-- ["primitive_types3.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types3.rs%0A%2F%2F+Create+an+array+with+at+least+100+elements+in+it+where+the+%3F%3F%3F+is.+%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+a+%3D+%3F%3F%3F%0A%0A++++if+a.len%28%29+%3E%3D+100+%7B%0A++++++++println%21%28%22Wow%2C+that%27s+a+big+array%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Meh%2C+I+eat+arrays+like+that+for+breakfast.%22%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+There%27s+a+shorthand+to+initialize+Arrays+with+a+certain+size+that+does+not+%0A%2F%2F+require+you+to+type+in+100+items+%28but+you+certainly+can+if+you+want%21%29%0A%2F%2F+Check+out+the+Primitive+Types+-%3E+Arrays+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch03-02-data-types.html%23arrays%0A%2F%2F+Bonus%3A+what+are+some+other+things+you+could+have+that+would+return+true%0A%2F%2F+for+%60a.len%28%29+%3E%3D+100%60%3F%0A)
-- ["primitive_types4.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types4.rs%0A%2F%2F+Get+a+slice+out+of+Array+a+where+the+%3F%3F%3F+is+so+that+the+%60if%60+statement%0A%2F%2F+returns+true.+Scroll+down+for+hints%21%21%0A%0Afn+main%28%29+%7B%0A++++let+a+%3D+%5B1%2C+2%2C+3%2C+4%2C+5%5D%3B%0A%0A++++let+nice_slice+%3D+%3F%3F%3F%0A%0A++++if+nice_slice+%3D%3D+%5B2%2C+3%2C+4%5D+%7B%0A++++++++println%21%28%22Nice+slice%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Not+quite+what+I+was+expecting...+I+see%3A+%7B%3A%3F%7D%22%2C+nice_slice%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Take+a+look+at+the+Primitive+Types+-%3E+Slices+section+of+the+book%3A%0A%2F%2F+http%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fprimitive-types.html%23slices%0A%2F%2F+and+use+the+starting+and+ending+indices+of+the+items+in+the+Array%0A%2F%2F+that+you+want+to+end+up+in+the+slice.%0A%0A%2F%2F+If+you%27re+curious+why+the+right+hand+of+the+%60%3D%3D%60+comparison+does+not%0A%2F%2F+have+an+ampersand+for+a+reference+since+the+left+hand+side+is+a%0A%2F%2F+reference%2C+take+a+look+at+the+Deref+coercions+chapter%3A%0A%2F%2F+http%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fderef-coercions.html%0A)
-- ["primitive_types5.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types5.rs%0A%2F%2F+Destructure+the+%60cat%60+tuple+so+that+the+println+will+work.%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+cat+%3D+%28%22Furry+McFurson%22%2C+3.5%29%3B%0A++++let+%2F*+your+pattern+here+*%2F+%3D+cat%3B%0A%0A++++println%21%28%22%7B%7D+is+%7B%7D+years+old.%22%2C+name%2C+age%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Take+a+look+at+the+Primitive+Types+-%3E+Tuples+section+of+the+book%3A%0A%2F%2F+http%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fprimitive-types.html%23tuples%0A%2F%2F+Particularly+the+part+about+%22destructuring+lets%22.+You%27ll+need+to%0A%2F%2F+make+a+pattern+to+bind+%60name%60+and+%60age%60+to+the+appropriate+parts%0A%2F%2F+of+the+tuple.+You+can+do+it%21%21%0A)
-- ["primitive_types6.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types6.rs%0A%2F%2F+Use+a+tuple+index+to+access+the+second+element+of+%60numbers%60.%0A%2F%2F+You+can+put+this+right+into+the+%60println%21%60+where+the+%3F%3F%3F+is.%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+numbers+%3D+%281%2C+2%2C+3%29%3B%0A++++println%21%28%22The+second+number+is+%7B%7D%22%2C+%3F%3F%3F%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+While+you+could+use+a+destructuring+%60let%60+for+the+tuple+here%2C+try+%0A%2F%2F+indexing+into+it+instead%2C+as+explained+here%3A%0A%2F%2F+http%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fprimitive-types.html%23tuple-indexing%0A%2F%2F+Now+you+have+another+tool+in+your+toolbox%21%0A)
+- ["primitive_types3.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types3.rs%0A%2F%2F+Create+an+array+with+at+least+100+elements+in+it+where+the+%3F%3F%3F+is.+%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+a+%3D+%3F%3F%3F%0A%0A++++if+a.len%28%29+%3E%3D+100+%7B%0A++++++++println%21%28%22Wow%2C+that%27s+a+big+array%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Meh%2C+I+eat+arrays+like+that+for+breakfast.%22%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+There%27s+a+shorthand+to+initialize+Arrays+with+a+certain+size+that+does+not+%0A%2F%2F+require+you+to+type+in+100+items+%28but+you+certainly+can+if+you+want%21%29.%0A%2F%2F+For+example%2C+you+can+do%3A%0A%2F%2F+let+array+%3D+%5B%22Are+we+there+yet%3F%22%3B+10%5D%3B%0A%0A%2F%2F+Bonus%3A+what+are+some+other+things+you+could+have+that+would+return+true%0A%2F%2F+for+%60a.len%28%29+%3E%3D+100%60%3F%0A)
+- ["primitive_types4.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types4.rs%0A%2F%2F+Get+a+slice+out+of+Array+a+where+the+%3F%3F%3F+is+so+that+the+%60if%60+statement%0A%2F%2F+returns+true.+Scroll+down+for+hints%21%21%0A%0Afn+main%28%29+%7B%0A++++let+a+%3D+%5B1%2C+2%2C+3%2C+4%2C+5%5D%3B%0A%0A++++let+nice_slice+%3D+%3F%3F%3F%0A%0A++++if+nice_slice+%3D%3D+%5B2%2C+3%2C+4%5D+%7B%0A++++++++println%21%28%22Nice+slice%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Not+quite+what+I+was+expecting...+I+see%3A+%7B%3A%3F%7D%22%2C+nice_slice%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Take+a+look+at+the+Understanding+Ownership+-%3E+Slices+-%3E+Other+Slices+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch04-03-slices.html%23other-slices%0A%2F%2F+and+use+the+starting+and+ending+indices+of+the+items+in+the+Array%0A%2F%2F+that+you+want+to+end+up+in+the+slice.%0A%0A%2F%2F+If+you%27re+curious+why+the+right+hand+of+the+%60%3D%3D%60+comparison+does+not%0A%2F%2F+have+an+ampersand+for+a+reference+since+the+left+hand+side+is+a%0A%2F%2F+reference%2C+take+a+look+at+the+Deref+coercions+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch15-02-deref.html%23implicit-deref-coercions-with-functions-and-methods%0A)
+- ["primitive_types5.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types5.rs%0A%2F%2F+Destructure+the+%60cat%60+tuple+so+that+the+println+will+work.%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+cat+%3D+%28%22Furry+McFurson%22%2C+3.5%29%3B%0A++++let+%2F*+your+pattern+here+*%2F+%3D+cat%3B%0A%0A++++println%21%28%22%7B%7D+is+%7B%7D+years+old.%22%2C+name%2C+age%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Take+a+look+at+the+Data+Types+-%3E+The+Tuple+Type+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch03-02-data-types.html%23the-tuple-type%0A%2F%2F+Particularly+the+part+about+destructuring+%28second+to+last+example+in+the+section%29.+%0A%2F%2F+You%27ll+need+to+make+a+pattern+to+bind+%60name%60+and+%60age%60+to+the+appropriate+parts%0A%2F%2F+of+the+tuple.+You+can+do+it%21%21%0A)
+- ["primitive_types6.rs"](https://play.rust-lang.org/?code=%2F%2F+primitive_types6.rs%0A%2F%2F+Use+a+tuple+index+to+access+the+second+element+of+%60numbers%60.%0A%2F%2F+You+can+put+this+right+into+the+%60println%21%60+where+the+%3F%3F%3F+is.%0A%2F%2F+Scroll+down+for+hints%21%0A%0Afn+main%28%29+%7B%0A++++let+numbers+%3D+%281%2C+2%2C+3%29%3B%0A++++println%21%28%22The+second+number+is+%7B%7D%22%2C+%3F%3F%3F%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+While+you+could+use+a+destructuring+%60let%60+for+the+tuple+here%2C+try+%0A%2F%2F+indexing+into+it+instead%2C+as+explained+in+the+last+example+of+the+%0A%2F%2F+Data+Types+-%3E+The+Tuple+Type+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch03-02-data-types.html%23the-tuple-type%0A%2F%2F+Now+you+have+another+tool+in+your+toolbox%21%0A)
 
 ### Tests
 
@@ -138,9 +138,9 @@ relevant.
 - ["option1.rs"](https://play.rust-lang.org/?code=%2F%2F+option1.rs%0A%2F%2F+This+example+panics+because+the+second+time+it+calls+%60pop%60%2C+the+%60vec%60%0A%2F%2F+is+empty%2C+so+%60pop%60+returns+%60None%60%2C+and+%60unwrap%60+panics+if+it%27s+called%0A%2F%2F+on+%60None%60.+Handle+this+in+a+more+graceful+way+than+calling+%60unwrap%60%21%0A%2F%2F+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+mut+list+%3D+vec%21%5B3%5D%3B%0A%0A++++let+last+%3D+list.pop%28%29.unwrap%28%29%3B%0A++++println%21%28%22The+last+item+in+the+list+is+%7B%3A%3F%7D%22%2C+last%29%3B%0A%0A++++let+second_to_last+%3D+list.pop%28%29.unwrap%28%29%3B%0A++++println%21%28%22The+second-to-last+item+in+the+list+is+%7B%3A%3F%7D%22%2C+second_to_last%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Try+using+a+%60match%60+statement+where+the+arms+are+%60Some%28thing%29%60+and+%60None%60.%0A%2F%2F+Or+set+a+default+value+to+print+out+if+you+get+%60None%60+by+using+the%0A%2F%2F+function+%60unwrap_or%60.%0A%2F%2F+Or+use+an+%60if+let%60+statement+on+the+result+of+%60pop%28%29%60+to+both+destructure%0A%2F%2F+a+%60Some%60+value+and+only+print+out+something+if+we+have+a+value%21%0A)
 - ["result1.rs"](https://play.rust-lang.org/?code=%2F%2F+result1.rs%0A%2F%2F+Make+this+test+pass%21+Scroll+down+for+hints+%3A%29%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Astruct+PositiveNonzeroInteger%28u64%29%3B%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Aenum+CreationError+%7B%0A++++Negative%2C%0A++++Zero%2C%0A%7D%0A%0Aimpl+PositiveNonzeroInteger+%7B%0A++++fn+new%28value%3A+i64%29+-%3E+Result%3CPositiveNonzeroInteger%2C+CreationError%3E+%7B%0A++++++++Ok%28PositiveNonzeroInteger%28value+as+u64%29%29%0A++++%7D%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_creation%28%29+%7B%0A++++assert%21%28PositiveNonzeroInteger%3A%3Anew%2810%29.is_ok%28%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3ANegative%29%2C+PositiveNonzeroInteger%3A%3Anew%28-10%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3AZero%29%2C+PositiveNonzeroInteger%3A%3Anew%280%29%29%3B%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+%60PositiveNonzeroInteger%3A%3Anew%60+is+always+creating+a+new+instance+and+returning+an+%60Ok%60+result.%0A%2F%2F+It+should+be+doing+some+checking%2C+returning+an+%60Err%60+result+if+those+checks+fail%2C+and+only%0A%2F%2F+returning+an+%60Ok%60+result+if+those+checks+determine+that+everything+is...+okay+%3A%29%0A)
 - ["errors1.rs"](https://play.rust-lang.org/?code=%2F%2F+errors1.rs%0A%2F%2F+This+function+refuses+to+generate+text+to+be+printed+on+a+nametag+if%0A%2F%2F+you+pass+it+an+empty+string.+It%27d+be+nicer+if+it+explained+what+the+problem%0A%2F%2F+was%2C+instead+of+just+sometimes+returning+%60None%60.+The+2nd+test+currently%0A%2F%2F+does+not+compile+or+pass%2C+but+it+illustrates+the+behavior+we+would+like%0A%2F%2F+this+function+to+have.%0A%2F%2F+Scroll+down+for+hints%21%21%21%0A%0Apub+fn+generate_nametag_text%28name%3A+String%29+-%3E+Option%3CString%3E+%7B%0A++++if+name.len%28%29+%3E+0+%7B%0A++++++++Some%28format%21%28%22Hi%21+My+name+is+%7B%7D%22%2C+name%29%29%0A++++%7D+else+%7B%0A++++++++%2F%2F+Empty+names+aren%27t+allowed.%0A++++++++None%0A++++%7D%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%2F%2F+This+test+passes+initially+if+you+comment+out+the+2nd+test.%0A++++%2F%2F+You%27ll+need+to+update+what+this+test+expects+when+you+change%0A++++%2F%2F+the+function+under+test%21%0A++++%23%5Btest%5D%0A++++fn+generates_nametag_text_for_a_nonempty_name%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++generate_nametag_text%28%22Beyonc%C3%A9%22.into%28%29%29%2C%0A++++++++++++Some%28%22Hi%21+My+name+is+Beyonc%C3%A9%22.into%28%29%29%0A++++++++%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+explains_why_generating_nametag_text_fails%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++generate_nametag_text%28%22%22.into%28%29%29%2C%0A++++++++++++Err%28%22%60name%60+was+empty%3B+it+must+be+nonempty.%22.into%28%29%29%0A++++++++%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+%60Err%60+is+one+of+the+variants+of+%60Result%60%2C+so+what+the+2nd+test+is+saying%0A%2F%2F+is+that+%60generate_nametag_text%60+should+return+a+%60Result%60+instead+of+an%0A%2F%2F+%60Option%60.%0A%0A%2F%2F+To+make+this+change%2C+you%27ll+need+to%3A%0A%2F%2F+-+update+the+return+type+in+the+function+signature+to+be+a+Result+that%0A%2F%2F+++could+be+the+variants+%60Ok%28String%29%60+and+%60Err%28String%29%60%0A%2F%2F+-+change+the+body+of+the+function+to+return+%60Ok%28stuff%29%60+where+it+currently%0A%2F%2F+++returns+%60Some%28stuff%29%60%0A%2F%2F+-+change+the+body+of+the+function+to+return+%60Err%28error+message%29%60+where+it%0A%2F%2F+++currently+returns+%60None%60%0A%2F%2F+-+change+the+first+test+to+expect+%60Ok%28stuff%29%60+where+it+currently+expects%0A%2F%2F+++%60Some%28stuff%29%60.%0A)
-- ["errors2.rs"](https://play.rust-lang.org/?code=%2F%2F+errors2.rs%0A%2F%2F+Say+we%27re+writing+a+game+where+you+can+buy+items+with+tokens.+All+items+cost%0A%2F%2F+5+tokens%2C+and+whenever+you+purchase+items+there+is+a+processing+fee+of+1%0A%2F%2F+token.+A+player+of+the+game+will+type+in+how+many+items+they+want+to+buy%2C%0A%2F%2F+and+the+%60total_cost%60+function+will+calculate+the+total+number+of+tokens.%0A%2F%2F+Since+the+player+typed+in+the+quantity%2C+though%2C+we+get+it+as+a+string--+and%0A%2F%2F+they+might+have+typed+anything%2C+not+just+numbers%21%0A%0A%2F%2F+Right+now%2C+this+function+isn%27t+handling+the+error+case+at+all+%28and+isn%27t%0A%2F%2F+handling+the+success+case+properly+either%29.+What+we+want+to+do+is%3A%0A%2F%2F+if+we+call+the+%60parse%60+function+on+a+string+that+is+not+a+number%2C+that%0A%2F%2F+function+will+return+a+%60ParseIntError%60%2C+and+in+that+case%2C+we+want+to%0A%2F%2F+immediately+return+that+error+from+our+function+and+not+try+to+multiply%0A%2F%2F+and+add.%0A%0A%2F%2F+There+are+at+least+two+ways+to+implement+this+that+are+both+correct--+but%0A%2F%2F+one+is+a+lot+shorter%21+Scroll+down+for+hints+to+both+ways.%0A%0Ause+std%3A%3Anum%3A%3AParseIntError%3B%0A%0Apub+fn+total_cost%28item_quantity%3A+%26str%29+-%3E+Result%3Ci32%2C+ParseIntError%3E+%7B%0A++++let+processing_fee+%3D+1%3B%0A++++let+cost_per_item+%3D+5%3B%0A++++let+qty+%3D+item_quantity.parse%3A%3A%3Ci32%3E%28%29%3B%0A%0A++++Ok%28qty+*+cost_per_item+%2B+processing_fee%29%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%23%5Btest%5D%0A++++fn+item_quantity_is_a_valid_number%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++total_cost%28%2234%22%29%2C%0A++++++++++++Ok%28171%29%0A++++++++%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+item_quantity_is_an_invalid_number%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++total_cost%28%22beep+boop%22%29.unwrap_err%28%29.to_string%28%29%2C%0A++++++++++++%22invalid+digit+found+in+string%22%0A++++++++%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+One+way+to+handle+this+is+using+a+%60match%60+statement+on%0A%2F%2F+%60item_quantity.parse%3A%3A%3Ci32%3E%28%29%60+where+the+cases+are+%60Ok%28something%29%60+and%0A%2F%2F+%60Err%28something%29%60.+This+pattern+is+very+common+in+Rust%2C+though%2C+so+there%27s%0A%2F%2F+a+%60%3F%60+operator+that+does+pretty+much+what+you+would+make+that+match+statement%0A%2F%2F+do+for+you%21+Take+a+look+at+this+section+of+the+Error+Handling+chapter%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fbook%2Fsecond-edition%2Fch09-02-recoverable-errors-with-result.html%23a-shortcut-for-propagating-errors-%0A%2F%2F+and+give+it+a+try%21%0A)
+- ["errors2.rs"](https://play.rust-lang.org/?code=%2F%2F+errors2.rs%0A%2F%2F+Say+we%27re+writing+a+game+where+you+can+buy+items+with+tokens.+All+items+cost%0A%2F%2F+5+tokens%2C+and+whenever+you+purchase+items+there+is+a+processing+fee+of+1%0A%2F%2F+token.+A+player+of+the+game+will+type+in+how+many+items+they+want+to+buy%2C%0A%2F%2F+and+the+%60total_cost%60+function+will+calculate+the+total+number+of+tokens.%0A%2F%2F+Since+the+player+typed+in+the+quantity%2C+though%2C+we+get+it+as+a+string--+and%0A%2F%2F+they+might+have+typed+anything%2C+not+just+numbers%21%0A%0A%2F%2F+Right+now%2C+this+function+isn%27t+handling+the+error+case+at+all+%28and+isn%27t%0A%2F%2F+handling+the+success+case+properly+either%29.+What+we+want+to+do+is%3A%0A%2F%2F+if+we+call+the+%60parse%60+function+on+a+string+that+is+not+a+number%2C+that%0A%2F%2F+function+will+return+a+%60ParseIntError%60%2C+and+in+that+case%2C+we+want+to%0A%2F%2F+immediately+return+that+error+from+our+function+and+not+try+to+multiply%0A%2F%2F+and+add.%0A%0A%2F%2F+There+are+at+least+two+ways+to+implement+this+that+are+both+correct--+but%0A%2F%2F+one+is+a+lot+shorter%21+Scroll+down+for+hints+to+both+ways.%0A%0Ause+std%3A%3Anum%3A%3AParseIntError%3B%0A%0Apub+fn+total_cost%28item_quantity%3A+%26str%29+-%3E+Result%3Ci32%2C+ParseIntError%3E+%7B%0A++++let+processing_fee+%3D+1%3B%0A++++let+cost_per_item+%3D+5%3B%0A++++let+qty+%3D+item_quantity.parse%3A%3A%3Ci32%3E%28%29%3B%0A%0A++++Ok%28qty+*+cost_per_item+%2B+processing_fee%29%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%23%5Btest%5D%0A++++fn+item_quantity_is_a_valid_number%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++total_cost%28%2234%22%29%2C%0A++++++++++++Ok%28171%29%0A++++++++%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+item_quantity_is_an_invalid_number%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++total_cost%28%22beep+boop%22%29.unwrap_err%28%29.to_string%28%29%2C%0A++++++++++++%22invalid+digit+found+in+string%22%0A++++++++%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+One+way+to+handle+this+is+using+a+%60match%60+statement+on%0A%2F%2F+%60item_quantity.parse%3A%3A%3Ci32%3E%28%29%60+where+the+cases+are+%60Ok%28something%29%60+and%0A%2F%2F+%60Err%28something%29%60.+This+pattern+is+very+common+in+Rust%2C+though%2C+so+there%27s%0A%2F%2F+a+%60%3F%60+operator+that+does+pretty+much+what+you+would+make+that+match+statement%0A%2F%2F+do+for+you%21+Take+a+look+at+this+section+of+the+Error+Handling+chapter%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch09-02-recoverable-errors-with-result.html%23a-shortcut-for-propagating-errors-the--operator%0A%2F%2F+and+give+it+a+try%21%0A)
 - ["errors3.rs"](https://play.rust-lang.org/?code=%2F%2F+errors3.rs%0A%2F%2F+This+is+a+program+that+is+trying+to+use+a+completed+version+of+the%0A%2F%2F+%60total_cost%60+function+from+the+previous+exercise.+It%27s+not+working+though--%0A%2F%2F+we+can%27t+use+the+%60%3F%60+operator+in+the+%60main%28%29%60+function%21+Why+not%3F%0A%2F%2F+What+should+we+do+instead%3F+Scroll+for+hints%21%0A%0Ause+std%3A%3Anum%3A%3AParseIntError%3B%0A%0Afn+main%28%29+%7B%0A++++let+mut+tokens+%3D+100%3B%0A++++let+pretend_user_input+%3D+%228%22%3B%0A%0A++++let+cost+%3D+total_cost%28pretend_user_input%29%3F%3B%0A%0A++++if+cost+%3E+tokens+%7B%0A++++++++println%21%28%22You+can%27t+afford+that+many%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++tokens+-%3D+cost%3B%0A++++++++println%21%28%22You+now+have+%7B%7D+tokens.%22%2C+tokens%29%3B%0A++++%7D%0A%7D%0A%0Apub+fn+total_cost%28item_quantity%3A+%26str%29+-%3E+Result%3Ci32%2C+ParseIntError%3E+%7B%0A++++let+processing_fee+%3D+1%3B%0A++++let+cost_per_item+%3D+5%3B%0A++++let+qty+%3D+item_quantity.parse%3A%3A%3Ci32%3E%28%29%3F%3B%0A%0A++++Ok%28qty+*+cost_per_item+%2B+processing_fee%29%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Since+the+%60%3F%60+operator+returns+an+%60Err%60+early+if+the+thing+it%27s+trying+to%0A%2F%2F+do+fails%2C+you+can+only+use+the+%60%3F%60+operator+in+functions+that+have+a%0A%2F%2F+%60Result%60+as+their+return+type.%0A%0A%2F%2F+Hence+the+error+that+you+get+if+you+run+this+code+is%3A%0A%0A%2F%2F+%60%60%60%0A%2F%2F+error%5BE0277%5D%3A+the+%60%3F%60+operator+can+only+be+used+in+a+function+that+returns+%60Result%60+%28or+another+type+that+implements+%60std%3A%3Aops%3A%3ATry%60%29%0A%2F%2F+%60%60%60%0A%0A%2F%2F+So+we+have+to+use+another+way+of+handling+a+%60Result%60+within+%60main%60.%0A%0A%2F%2F+Decide+what+we+should+do+if+%60pretend_user_input%60+has+a+string+value+that+does%0A%2F%2F+not+parse+to+an+integer%2C+and+implement+that+instead+of+using+the+%60%3F%60%0A%2F%2F+operator.%0A)
-- ["errorsn.rs"](https://play.rust-lang.org/?code=%2F%2F+errorsn.rs%0A%2F%2F+This+is+a+bigger+error+exercise+than+the+previous+ones%21%0A%2F%2F+You+can+do+it%21+%3A%29%0A%2F%2F%0A%2F%2F+Edit+the+%60read_and_validate%60+function+so+that+it+compiles+and%0A%2F%2F+passes+the+tests...+so+many+things+could+go+wrong%21%0A%2F%2F%0A%2F%2F+-+Reading+from+stdin+could+produce+an+io%3A%3AError%0A%2F%2F+-+Parsing+the+input+could+produce+a+num%3A%3AParseIntError%0A%2F%2F+-+Validating+the+input+could+produce+a+CreationError+%28defined+below%29%0A%2F%2F%0A%2F%2F+How+can+we+lump+these+errors+into+one+general+error%3F+That+is%2C+what%0A%2F%2F+type+goes+where+the+question+marks+are%2C+and+how+do+we+return%0A%2F%2F+that+type+from+the+body+of+read_and_validate%3F%0A%2F%2F%0A%2F%2F+Scroll+down+for+hints+%3A%29%0A%0Ause+std%3A%3Aerror%3B%0Ause+std%3A%3Afmt%3B%0Ause+std%3A%3Aio%3B%0A%0A%2F%2F+PositiveNonzeroInteger+is+a+struct+defined+below+the+tests.%0Afn+read_and_validate%28b%3A+%26mut+io%3A%3ABufRead%29+-%3E+Result%3CPositiveNonzeroInteger%2C+%3F%3F%3F%3E+%7B%0A++++let+mut+line+%3D+String%3A%3Anew%28%29%3B%0A++++b.read_line%28%26mut+line%29%3B%0A++++let+num%3A+i64+%3D+line.trim%28%29.parse%28%29%3B%0A++++let+answer+%3D+PositiveNonzeroInteger%3A%3Anew%28num%29%3B%0A++++answer%0A%7D%0A%0A%2F%2F+This+is+a+test+helper+function+that+turns+a+%26str+into+a+BufReader.%0Afn+test_with_str%28s%3A+%26str%29+-%3E+Result%3CPositiveNonzeroInteger%2C+Box%3Cerror%3A%3AError%3E%3E+%7B%0A++++let+mut+b+%3D+io%3A%3ABufReader%3A%3Anew%28s.as_bytes%28%29%29%3B%0A++++read_and_validate%28%26mut+b%29%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_success%28%29+%7B%0A++++let+x+%3D+test_with_str%28%2242%5Cn%22%29%3B%0A++++assert_eq%21%28PositiveNonzeroInteger%2842%29%2C+x.unwrap%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_not_num%28%29+%7B%0A++++let+x+%3D+test_with_str%28%22eleven+billion%5Cn%22%29%3B%0A++++assert%21%28x.is_err%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_non_positive%28%29+%7B%0A++++let+x+%3D+test_with_str%28%22-40%5Cn%22%29%3B%0A++++assert%21%28x.is_err%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_ioerror%28%29+%7B%0A++++struct+Broken%3B%0A++++impl+io%3A%3ARead+for+Broken+%7B%0A++++++++fn+read%28%26mut+self%2C+_buf%3A+%26mut+%5Bu8%5D%29+-%3E+io%3A%3AResult%3Cusize%3E+%7B%0A++++++++++++Err%28io%3A%3AError%3A%3Anew%28io%3A%3AErrorKind%3A%3ABrokenPipe%2C+%22uh-oh%21%22%29%29%0A++++++++%7D%0A++++%7D%0A++++let+mut+b+%3D+io%3A%3ABufReader%3A%3Anew%28Broken%29%3B%0A++++assert%21%28read_and_validate%28%26mut+b%29.is_err%28%29%29%3B%0A++++assert_eq%21%28%22uh-oh%21%22%2C+read_and_validate%28%26mut+b%29.unwrap_err%28%29.to_string%28%29%29%3B%0A%7D%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Astruct+PositiveNonzeroInteger%28u64%29%3B%0A%0Aimpl+PositiveNonzeroInteger+%7B%0A++++fn+new%28value%3A+i64%29+-%3E+Result%3CPositiveNonzeroInteger%2C+CreationError%3E+%7B%0A++++++++if+value+%3D%3D+0+%7B%0A++++++++++++Err%28CreationError%3A%3AZero%29%0A++++++++%7D+else+if+value+%3C+0+%7B%0A++++++++++++Err%28CreationError%3A%3ANegative%29%0A++++++++%7D+else+%7B%0A++++++++++++Ok%28PositiveNonzeroInteger%28value+as+u64%29%29%0A++++++++%7D%0A++++%7D%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_positive_nonzero_integer_creation%28%29+%7B%0A++++assert%21%28PositiveNonzeroInteger%3A%3Anew%2810%29.is_ok%28%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3ANegative%29%2C+PositiveNonzeroInteger%3A%3Anew%28-10%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3AZero%29%2C+PositiveNonzeroInteger%3A%3Anew%280%29%29%3B%0A%7D%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Aenum+CreationError+%7B%0A++++Negative%2C%0A++++Zero%2C%0A%7D%0A%0Aimpl+fmt%3A%3ADisplay+for+CreationError+%7B%0A++++fn+fmt%28%26self%2C+f%3A+%26mut+fmt%3A%3AFormatter%29+-%3E+fmt%3A%3AResult+%7B%0A++++++++f.write_str%28%28self+as+%26error%3A%3AError%29.description%28%29%29%0A++++%7D%0A%7D%0A%0Aimpl+error%3A%3AError+for+CreationError+%7B%0A++++fn+description%28%26self%29+-%3E+%26str+%7B%0A++++++++match+*self+%7B%0A++++++++++++CreationError%3A%3ANegative+%3D%3E+%22Negative%22%2C%0A++++++++++++CreationError%3A%3AZero+%3D%3E+%22Zero%22%2C%0A++++++++%7D%0A++++%7D%0A%7D%0A%0A%2F%2F+First+hint%3A+To+figure+out+what+type+should+go+where+the+%3F%3F%3F+is%2C+take+a+look%0A%2F%2F+at+the+test+helper+function+%60test_with_str%60%2C+since+it+returns+whatever%0A%2F%2F+%60read_and_validate%60+returns+and%60test_with_str%60+has+its+signature+fully%0A%2F%2F+specified.%0A%0A%2F%2F+Next+hint%3A+There+are+three+places+in+%60read_and_validate%60+that+we+call+a%0A%2F%2F+function+that+returns+a+%60Result%60+%28that+is%2C+the+functions+might+fail%29.%0A%2F%2F+Apply+the+%60%3F%60+operator+on+those+calls+so+that+we+return+immediately+from%0A%2F%2F+%60read_and_validate%60+if+those+function+calls+fail.%0A%0A%2F%2F+Another+hint%3A+under+the+hood%2C+the+%60%3F%60+operator+calls+%60From%3A%3Afrom%60%0A%2F%2F+on+the+error+value+to+convert+it+to+a+boxed+trait+object%2C+a+Box%3Cerror%3A%3AError%3E%2C%0A%2F%2F+which+is+polymorphic--+that+means+that+lots+of+different+kinds+of+errors%0A%2F%2F+can+be+returned+from+the+same+function+because+all+errors+act+the+same%0A%2F%2F+since+they+all+implement+the+%60error%3A%3AError%60+trait.%0A%2F%2F+Check+out+this+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch09-02-recoverable-errors-with-result.html%23a-shortcut-for-propagating-errors-%0A%0A%2F%2F+Another+another+hint%3A+Note+that+because+the+%60%3F%60+operator+returns%0A%2F%2F+the+*unwrapped*+value+in+the+%60Ok%60+case%2C+if+we+want+to+return+a+%60Result%60+from%0A%2F%2F+%60read_and_validate%60+for+*its*+success+case%2C+we%27ll+have+to+rewrap+a+value%0A%2F%2F+that+we+got+from+the+return+value+of+a+%60%3F%60ed+call+in+an+%60Ok%60--+this+will%0A%2F%2F+look+like+%60Ok%28something%29%60.%0A%0A%2F%2F+Another+another+another+hint%3A+%60Result%60s+must+be+%22used%22%2C+that+is%2C+you%27ll%0A%2F%2F+get+a+warning+if+you+don%27t+handle+a+%60Result%60+that+you+get+in+your%0A%2F%2F+function.+Read+more+about+that+in+the+%60std%3A%3Aresult%60+module+docs%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstd%2Fresult%2F%23results-must-be-used%0A)
+- ["errorsn.rs"](https://play.rust-lang.org/?code=%2F%2F+errorsn.rs%0A%2F%2F+This+is+a+bigger+error+exercise+than+the+previous+ones%21%0A%2F%2F+You+can+do+it%21+%3A%29%0A%2F%2F%0A%2F%2F+Edit+the+%60read_and_validate%60+function+so+that+it+compiles+and%0A%2F%2F+passes+the+tests...+so+many+things+could+go+wrong%21%0A%2F%2F%0A%2F%2F+-+Reading+from+stdin+could+produce+an+io%3A%3AError%0A%2F%2F+-+Parsing+the+input+could+produce+a+num%3A%3AParseIntError%0A%2F%2F+-+Validating+the+input+could+produce+a+CreationError+%28defined+below%29%0A%2F%2F%0A%2F%2F+How+can+we+lump+these+errors+into+one+general+error%3F+That+is%2C+what%0A%2F%2F+type+goes+where+the+question+marks+are%2C+and+how+do+we+return%0A%2F%2F+that+type+from+the+body+of+read_and_validate%3F%0A%2F%2F%0A%2F%2F+Scroll+down+for+hints+%3A%29%0A%0Ause+std%3A%3Aerror%3B%0Ause+std%3A%3Afmt%3B%0Ause+std%3A%3Aio%3B%0A%0A%2F%2F+PositiveNonzeroInteger+is+a+struct+defined+below+the+tests.%0Afn+read_and_validate%28b%3A+%26mut+io%3A%3ABufRead%29+-%3E+Result%3CPositiveNonzeroInteger%2C+%3F%3F%3F%3E+%7B%0A++++let+mut+line+%3D+String%3A%3Anew%28%29%3B%0A++++b.read_line%28%26mut+line%29%3B%0A++++let+num%3A+i64+%3D+line.trim%28%29.parse%28%29%3B%0A++++let+answer+%3D+PositiveNonzeroInteger%3A%3Anew%28num%29%3B%0A++++answer%0A%7D%0A%0A%2F%2F+This+is+a+test+helper+function+that+turns+a+%26str+into+a+BufReader.%0Afn+test_with_str%28s%3A+%26str%29+-%3E+Result%3CPositiveNonzeroInteger%2C+Box%3Cerror%3A%3AError%3E%3E+%7B%0A++++let+mut+b+%3D+io%3A%3ABufReader%3A%3Anew%28s.as_bytes%28%29%29%3B%0A++++read_and_validate%28%26mut+b%29%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_success%28%29+%7B%0A++++let+x+%3D+test_with_str%28%2242%5Cn%22%29%3B%0A++++assert_eq%21%28PositiveNonzeroInteger%2842%29%2C+x.unwrap%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_not_num%28%29+%7B%0A++++let+x+%3D+test_with_str%28%22eleven+billion%5Cn%22%29%3B%0A++++assert%21%28x.is_err%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_non_positive%28%29+%7B%0A++++let+x+%3D+test_with_str%28%22-40%5Cn%22%29%3B%0A++++assert%21%28x.is_err%28%29%29%3B%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_ioerror%28%29+%7B%0A++++struct+Broken%3B%0A++++impl+io%3A%3ARead+for+Broken+%7B%0A++++++++fn+read%28%26mut+self%2C+_buf%3A+%26mut+%5Bu8%5D%29+-%3E+io%3A%3AResult%3Cusize%3E+%7B%0A++++++++++++Err%28io%3A%3AError%3A%3Anew%28io%3A%3AErrorKind%3A%3ABrokenPipe%2C+%22uh-oh%21%22%29%29%0A++++++++%7D%0A++++%7D%0A++++let+mut+b+%3D+io%3A%3ABufReader%3A%3Anew%28Broken%29%3B%0A++++assert%21%28read_and_validate%28%26mut+b%29.is_err%28%29%29%3B%0A++++assert_eq%21%28%22uh-oh%21%22%2C+read_and_validate%28%26mut+b%29.unwrap_err%28%29.to_string%28%29%29%3B%0A%7D%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Astruct+PositiveNonzeroInteger%28u64%29%3B%0A%0Aimpl+PositiveNonzeroInteger+%7B%0A++++fn+new%28value%3A+i64%29+-%3E+Result%3CPositiveNonzeroInteger%2C+CreationError%3E+%7B%0A++++++++if+value+%3D%3D+0+%7B%0A++++++++++++Err%28CreationError%3A%3AZero%29%0A++++++++%7D+else+if+value+%3C+0+%7B%0A++++++++++++Err%28CreationError%3A%3ANegative%29%0A++++++++%7D+else+%7B%0A++++++++++++Ok%28PositiveNonzeroInteger%28value+as+u64%29%29%0A++++++++%7D%0A++++%7D%0A%7D%0A%0A%23%5Btest%5D%0Afn+test_positive_nonzero_integer_creation%28%29+%7B%0A++++assert%21%28PositiveNonzeroInteger%3A%3Anew%2810%29.is_ok%28%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3ANegative%29%2C+PositiveNonzeroInteger%3A%3Anew%28-10%29%29%3B%0A++++assert_eq%21%28Err%28CreationError%3A%3AZero%29%2C+PositiveNonzeroInteger%3A%3Anew%280%29%29%3B%0A%7D%0A%0A%23%5Bderive%28PartialEq%2CDebug%29%5D%0Aenum+CreationError+%7B%0A++++Negative%2C%0A++++Zero%2C%0A%7D%0A%0Aimpl+fmt%3A%3ADisplay+for+CreationError+%7B%0A++++fn+fmt%28%26self%2C+f%3A+%26mut+fmt%3A%3AFormatter%29+-%3E+fmt%3A%3AResult+%7B%0A++++++++f.write_str%28%28self+as+%26error%3A%3AError%29.description%28%29%29%0A++++%7D%0A%7D%0A%0Aimpl+error%3A%3AError+for+CreationError+%7B%0A++++fn+description%28%26self%29+-%3E+%26str+%7B%0A++++++++match+*self+%7B%0A++++++++++++CreationError%3A%3ANegative+%3D%3E+%22Negative%22%2C%0A++++++++++++CreationError%3A%3AZero+%3D%3E+%22Zero%22%2C%0A++++++++%7D%0A++++%7D%0A%7D%0A%0A%2F%2F+First+hint%3A+To+figure+out+what+type+should+go+where+the+%3F%3F%3F+is%2C+take+a+look%0A%2F%2F+at+the+test+helper+function+%60test_with_str%60%2C+since+it+returns+whatever%0A%2F%2F+%60read_and_validate%60+returns+and%60test_with_str%60+has+its+signature+fully%0A%2F%2F+specified.%0A%0A%2F%2F+Next+hint%3A+There+are+three+places+in+%60read_and_validate%60+that+we+call+a%0A%2F%2F+function+that+returns+a+%60Result%60+%28that+is%2C+the+functions+might+fail%29.%0A%2F%2F+Apply+the+%60%3F%60+operator+on+those+calls+so+that+we+return+immediately+from%0A%2F%2F+%60read_and_validate%60+if+those+function+calls+fail.%0A%0A%2F%2F+Another+hint%3A+under+the+hood%2C+the+%60%3F%60+operator+calls+%60From%3A%3Afrom%60%0A%2F%2F+on+the+error+value+to+convert+it+to+a+boxed+trait+object%2C+a+Box%3Cerror%3A%3AError%3E%2C%0A%2F%2F+which+is+polymorphic--+that+means+that+lots+of+different+kinds+of+errors%0A%2F%2F+can+be+returned+from+the+same+function+because+all+errors+act+the+same%0A%2F%2F+since+they+all+implement+the+%60error%3A%3AError%60+trait.%0A%2F%2F+Check+out+this+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch09-02-recoverable-errors-with-result.html%23a-shortcut-for-propagating-errors-the--operator%0A%0A%2F%2F+Another+another+hint%3A+Note+that+because+the+%60%3F%60+operator+returns%0A%2F%2F+the+*unwrapped*+value+in+the+%60Ok%60+case%2C+if+we+want+to+return+a+%60Result%60+from%0A%2F%2F+%60read_and_validate%60+for+*its*+success+case%2C+we%27ll+have+to+rewrap+a+value%0A%2F%2F+that+we+got+from+the+return+value+of+a+%60%3F%60ed+call+in+an+%60Ok%60--+this+will%0A%2F%2F+look+like+%60Ok%28something%29%60.%0A%0A%2F%2F+Another+another+another+hint%3A+%60Result%60s+must+be+%22used%22%2C+that+is%2C+you%27ll%0A%2F%2F+get+a+warning+if+you+don%27t+handle+a+%60Result%60+that+you+get+in+your%0A%2F%2F+function.+Read+more+about+that+in+the+%60std%3A%3Aresult%60+module+docs%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstd%2Fresult%2F%23results-must-be-used%0A)
 
 ### Standard library types
 
@@ -160,7 +160,7 @@ Check out the [Iterators chapter of the
 book](https://doc.rust-lang.org/book/second-edition/ch13-02-iterators.html) and the [Iterator
 docs](https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html).
 
-- ["iterator3.rs"](https://play.rust-lang.org/?code=%2F%2F+iterator3.rs%0A%2F%2F+This+is+a+bigger+exercise+than+most+of+the+others%21+You+can+do+it%21%0A%2F%2F+Here+is+your+mission%2C+should+you+choose+to+accept+it%3A%0A%2F%2F+1.+Complete+the+divide+function+to+get+the+first+four+tests+to+pass%0A%2F%2F+2.+Uncomment+the+last+two+tests+and+get+them+to+pass+by+filling+in%0A%2F%2F++++values+for+%60x%60+using+%60division_results%60.%0A%2F%2F+Scroll+down+for+a+minor+hint+for+part+2%2C+and+scroll+down+further+for%0A%2F%2F+a+major+hint.%0A%2F%2F+Have+fun+%3A-%29%0A%0A%23%5Bderive%28Debug%2C+PartialEq%2C+Eq%29%5D%0Apub+enum+DivisionError+%7B%0A++++NotDivisible%28NotDivisibleError%29%2C%0A++++DivideByZero%2C%0A%7D%0A%0A%23%5Bderive%28Debug%2C+PartialEq%2C+Eq%29%5D%0Apub+struct+NotDivisibleError+%7B%0A++++dividend%3A+i32%2C%0A++++divisor%3A+i32%2C%0A%7D%0A%0A%2F%2F+This+function+should+calculate+%60a%60+divided+by+%60b%60+if+%60a%60+is%0A%2F%2F+evenly+divisible+by+b.%0A%2F%2F+Otherwise%2C+it+should+return+a+suitable+error.%0Apub+fn+divide%28a%3A+i32%2C+b%3A+i32%29+-%3E+Result%3Ci32%2C+DivisionError%3E+%7B%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%2F%2F+Tests+that+verify+your+%60divide%60+function+implementation%0A++++%23%5Btest%5D%0A++++fn+test_success%28%29+%7B%0A++++++++assert_eq%21%28divide%2881%2C+9%29%2C+Ok%289%29%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_not_divisible%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++divide%2881%2C+6%29%2C%0A++++++++++++Err%28DivisionError%3A%3ANotDivisible%28NotDivisibleError%7B%0A++++++++++++++++dividend%3A+81%2C%0A++++++++++++++++divisor%3A+6%0A++++++++++++%7D%29%29%0A++++++++%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_divide_by_0%28%29+%7B%0A++++++++assert_eq%21%28divide%2881%2C+0%29%2C+Err%28DivisionError%3A%3ADivideByZero%29%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_divide_0_by_something%28%29+%7B%0A++++++++assert_eq%21%28divide%280%2C+81%29%2C+Ok%280%29%29%3B%0A++++%7D%0A%0A++++%2F%2F+Iterator+exercises+using+your+%60divide%60+function%0A++++%2F*%0A++++%23%5Btest%5D%0A++++fn+result_with_list%28%29+%7B%0A++++++++let+numbers+%3D+vec%21%5B27%2C+297%2C+38502%2C+81%5D%3B%0A++++++++let+division_results+%3D+numbers.into_iter%28%29.map%28%7Cn%7C+divide%28n%2C+27%29%29%3B%0A++++++++let+x+%2F%2F...+Fill+in+here%21%0A++++++++assert_eq%21%28format%21%28%22%7B%3A%3F%7D%22%2C+x%29%2C+%22Ok%28%5B1%2C+11%2C+1426%2C+3%5D%29%22%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+list_of_results%28%29+%7B%0A++++++++let+numbers+%3D+vec%21%5B27%2C+297%2C+38502%2C+81%5D%3B%0A++++++++let+division_results+%3D+numbers.into_iter%28%29.map%28%7Cn%7C+divide%28n%2C+27%29%29%3B%0A++++++++let+x+%2F%2F...+Fill+in+here%21%0A++++++++assert_eq%21%28format%21%28%22%7B%3A%3F%7D%22%2C+x%29%2C+%22%5BOk%281%29%2C+Ok%2811%29%2C+Ok%281426%29%2C+Ok%283%29%5D%22%29%3B%0A++++%7D%0A++++*%2F%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Minor+hint%3A+In+each+of+the+two+cases+in+the+match+in+main%2C+you+can+create+x+with+either+a+%27turbofish%27+or+by+hinting+the+type+of+x+to+the+compiler.+You+may+try+both.%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Major+hint%3A+Have+a+look+at+the+Iter+trait+and+at+the+explanation+of+its+collect+function.+Especially+the+part+about+Result+is+interesting.%0A)
+- ["iterator3.rs"](https://play.rust-lang.org/?code=%2F%2F+iterator3.rs%0A%2F%2F+This+is+a+bigger+exercise+than+most+of+the+others%21+You+can+do+it%21%0A%2F%2F+Here+is+your+mission%2C+should+you+choose+to+accept+it%3A%0A%2F%2F+1.+Complete+the+divide+function+to+get+the+first+four+tests+to+pass%0A%2F%2F+2.+Uncomment+the+last+two+tests+and+get+them+to+pass+by+filling+in%0A%2F%2F++++values+for+%60x%60+using+%60division_results%60.%0A%2F%2F+Scroll+down+for+a+minor+hint+for+part+2%2C+and+scroll+down+further+for%0A%2F%2F+a+major+hint.%0A%2F%2F+Have+fun+%3A-%29%0A%0A%23%5Bderive%28Debug%2C+PartialEq%2C+Eq%29%5D%0Apub+enum+DivisionError+%7B%0A++++NotDivisible%28NotDivisibleError%29%2C%0A++++DivideByZero%2C%0A%7D%0A%0A%23%5Bderive%28Debug%2C+PartialEq%2C+Eq%29%5D%0Apub+struct+NotDivisibleError+%7B%0A++++dividend%3A+i32%2C%0A++++divisor%3A+i32%2C%0A%7D%0A%0A%2F%2F+This+function+should+calculate+%60a%60+divided+by+%60b%60+if+%60a%60+is%0A%2F%2F+evenly+divisible+by+b.%0A%2F%2F+Otherwise%2C+it+should+return+a+suitable+error.%0Apub+fn+divide%28a%3A+i32%2C+b%3A+i32%29+-%3E+Result%3Ci32%2C+DivisionError%3E+%7B%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%2F%2F+Tests+that+verify+your+%60divide%60+function+implementation%0A++++%23%5Btest%5D%0A++++fn+test_success%28%29+%7B%0A++++++++assert_eq%21%28divide%2881%2C+9%29%2C+Ok%289%29%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_not_divisible%28%29+%7B%0A++++++++assert_eq%21%28%0A++++++++++++divide%2881%2C+6%29%2C%0A++++++++++++Err%28DivisionError%3A%3ANotDivisible%28NotDivisibleError%7B%0A++++++++++++++++dividend%3A+81%2C%0A++++++++++++++++divisor%3A+6%0A++++++++++++%7D%29%29%0A++++++++%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_divide_by_0%28%29+%7B%0A++++++++assert_eq%21%28divide%2881%2C+0%29%2C+Err%28DivisionError%3A%3ADivideByZero%29%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+test_divide_0_by_something%28%29+%7B%0A++++++++assert_eq%21%28divide%280%2C+81%29%2C+Ok%280%29%29%3B%0A++++%7D%0A%0A++++%2F%2F+Iterator+exercises+using+your+%60divide%60+function%0A++++%2F*%0A++++%23%5Btest%5D%0A++++fn+result_with_list%28%29+%7B%0A++++++++let+numbers+%3D+vec%21%5B27%2C+297%2C+38502%2C+81%5D%3B%0A++++++++let+division_results+%3D+numbers.into_iter%28%29.map%28%7Cn%7C+divide%28n%2C+27%29%29%3B%0A++++++++let+x+%2F%2F...+Fill+in+here%21%0A++++++++assert_eq%21%28format%21%28%22%7B%3A%3F%7D%22%2C+x%29%2C+%22Ok%28%5B1%2C+11%2C+1426%2C+3%5D%29%22%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+list_of_results%28%29+%7B%0A++++++++let+numbers+%3D+vec%21%5B27%2C+297%2C+38502%2C+81%5D%3B%0A++++++++let+division_results+%3D+numbers.into_iter%28%29.map%28%7Cn%7C+divide%28n%2C+27%29%29%3B%0A++++++++let+x+%2F%2F...+Fill+in+here%21%0A++++++++assert_eq%21%28format%21%28%22%7B%3A%3F%7D%22%2C+x%29%2C+%22%5BOk%281%29%2C+Ok%2811%29%2C+Ok%281426%29%2C+Ok%283%29%5D%22%29%3B%0A++++%7D%0A++++*%2F%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Minor+hint%3A+In+each+of+the+two+cases+in+the+match+in+main%2C+you+can+create+x+with+either+%0A%2F%2F+a+%27turbofish%27+or+by+hinting+the+type+of+x+to+the+compiler.+You+may+try+both.%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Major+hint%3A+Have+a+look+at+the+Iter+trait+and+at+the+explanation+of+its+collect+function.+%0A%2F%2F+Especially+the+part+about+Result+is+interesting.%0A)
 - ["iterators4.rs"](https://play.rust-lang.org/?code=%2F%2F+iterators4.rs%0A%0Apub+fn+factorial%28num%3A+u64%29+-%3E+u64+%7B%0A++++%2F%2F+Complete+this+function+to+return+factorial+of+num%0A++++%2F%2F+Do+not+use%3A%0A++++%2F%2F+-+return%0A++++%2F%2F+For+extra+fun+don%27t+use%3A%0A++++%2F%2F+-+imperative+style+loops+%28for%2C+while%29%0A++++%2F%2F+-+additional+variables%0A++++%2F%2F+For+the+most+fun+don%27t+use%3A%0A++++%2F%2F+-+recursion%0A++++%2F%2F+Scroll+down+for+hints.%0A%7D%0A%0A%23%5Bcfg%28test%29%5D%0Amod+tests+%7B%0A++++use+super%3A%3A*%3B%0A%0A++++%23%5Btest%5D%0A++++fn+factorial_of_1%28%29+%7B%0A++++++++assert_eq%21%281%2C+factorial%281%29%29%3B%0A++++%7D%0A++++%23%5Btest%5D%0A++++fn+factorial_of_2%28%29+%7B%0A++++++++assert_eq%21%282%2C+factorial%282%29%29%3B%0A++++%7D%0A%0A++++%23%5Btest%5D%0A++++fn+factorial_of_4%28%29+%7B%0A++++++++assert_eq%21%2824%2C+factorial%284%29%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+In+an+imperative+language+you+might+write+a+for+loop+to+iterate+through%0A%2F%2F+multiply+the+values+into+a+mutable+variable.+Or+you+might+write+code+more%0A%2F%2F+functionally+with+recursion+and+a+match+clause.+But+you+can+also+use+ranges%0A%2F%2F+and+iterators+to+solve+this+in+rust.%0A)
 
 ### Threads
@@ -170,7 +170,7 @@ example](https://doc.rust-lang.org/1.4.0/book/first-edition/dining-philosophers.
 [Concurrency Chapter](https://doc.rust-lang.org/book/second-edition/ch16-01-threads.html) from the
 book.
 
-- ["threads1.rs"](https://play.rust-lang.org/?code=%2F%2F+threads1.rs%0A%2F%2F+Make+this+compile%21+Scroll+down+for+hints+%3A%29+The+idea+is+the+thread%0A%2F%2F+spawned+on+line+19+is+completing+jobs+while+the+main+thread+is%0A%2F%2F+monitoring+progress+until+10+jobs+are+completed.+If+you+see+6+lines%0A%2F%2F+of+%22waiting...%22+and+the+program+ends+without+timing+out+the+playground%2C%0A%2F%2F+you%27ve+got+it+%3A%29%0A%0Ause+std%3A%3Async%3A%3AArc%3B%0Ause+std%3A%3Athread%3B%0Ause+std%3A%3Atime%3A%3ADuration%3B%0A%0Astruct+JobStatus+%7B%0A++++jobs_completed%3A+u32%2C%0A%7D%0A%0Afn+main%28%29+%7B%0A++++let+status+%3D+Arc%3A%3Anew%28JobStatus+%7B+jobs_completed%3A+0+%7D%29%3B%0A++++let+status_shared+%3D+status.clone%28%29%3B%0A++++thread%3A%3Aspawn%28move+%7C%7C+%7B%0A++++++++for+_+in+0..10+%7B%0A++++++++++++thread%3A%3Asleep%28Duration%3A%3Afrom_millis%28250%29%29%3B%0A++++++++++++status_shared.jobs_completed+%2B%3D+1%3B%0A++++++++%7D%0A++++%7D%29%3B%0A++++while+status.jobs_completed+%3C+10+%7B%0A++++++++println%21%28%22waiting...+%22%29%3B%0A++++++++thread%3A%3Asleep%28Duration%3A%3Afrom_millis%28500%29%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+%60Arc%60+is+an+Atomic+Reference+Counted+pointer+that+allows+safe%2C+shared+access%0A%2F%2F+to+**immutable**+data.+But+we+want+to+*change*+the+number+of+%60jobs_completed%60%0A%2F%2F+so+we%27ll+need+to+also+use+another+type+that+will+only+allow+one+thread+to%0A%2F%2F+mutate+the+data+at+a+time.+Take+a+look+at+this+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fconcurrency.html%23safe-shared-mutable-state%0A%2F%2F+and+keep+scrolling+if+you%27d+like+more+hints+%3A%29%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Do+you+now+have+an+%60Arc%60+%60Mutex%60+%60JobStatus%60+at+the+beginning+of+main%3F+Like%3A%0A%2F%2F+%60let+status+%3D+Arc%3A%3Anew%28Mutex%3A%3Anew%28JobStatus+%7B+jobs_completed%3A+0+%7D%29%29%3B%60%0A%2F%2F+Similar+to+the+code+in+the+example+in+the+book+that+happens+after+the+text%0A%2F%2F+that+says+%22We+can+use+Arc%3CT%3E+to+fix+this.%22.+If+not%2C+give+that+a+try%21+If+you%0A%2F%2F+do+and+would+like+more+hints%2C+keep+scrolling%21%21%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Make+sure+neither+of+your+threads+are+holding+onto+the+lock+of+the+mutex%0A%2F%2F+while+they+are+sleeping%2C+since+this+will+prevent+the+other+thread+from%0A%2F%2F+being+allowed+to+get+the+lock.+Locks+are+automatically+released+when%0A%2F%2F+they+go+out+of+scope.%0A%0A%2F%2F+Ok%2C+so%2C+real+talk%2C+this+was+actually+tricky+for+*me*+to+do+too.+And%0A%2F%2F+I+could+see+a+lot+of+different+problems+you+might+run+into%2C+so+at+this%0A%2F%2F+point+I%27m+not+sure+which+one+you%27ve+hit+%3A%29+Please+see+a+few+possible%0A%2F%2F+answers+on+https%3A%2F%2Fgithub.com%2Fcarols10cents%2Frustlings%2Fissues%2F3+--%0A%2F%2F+mine+is+a+little+more+complicated+because+I+decided+I+wanted+to+see%0A%2F%2F+the+number+of+jobs+currently+done+when+I+was+checking+the+status.%0A%0A%2F%2F+Please+open+an+issue+if+you%27re+still+running+into+a+problem+that%0A%2F%2F+these+hints+are+not+helping+you+with%2C+or+if+you%27ve+looked+at+the+sample%0A%2F%2F+answers+and+don%27t+understand+why+they+work+and+yours+doesn%27t.%0A%0A%2F%2F+If+you%27ve+learned+from+the+sample+solutions%2C+I+encourage+you+to+come%0A%2F%2F+back+to+this+exercise+and+try+it+again+in+a+few+days+to+reinforce%0A%2F%2F+what+you%27ve+learned+%3A%29%0A)
+- ["threads1.rs"](https://play.rust-lang.org/?code=%2F%2F+threads1.rs%0A%2F%2F+Make+this+compile%21+Scroll+down+for+hints+%3A%29+The+idea+is+the+thread%0A%2F%2F+spawned+on+line+19+is+completing+jobs+while+the+main+thread+is%0A%2F%2F+monitoring+progress+until+10+jobs+are+completed.+If+you+see+6+lines%0A%2F%2F+of+%22waiting...%22+and+the+program+ends+without+timing+out+the+playground%2C%0A%2F%2F+you%27ve+got+it+%3A%29%0A%0Ause+std%3A%3Async%3A%3AArc%3B%0Ause+std%3A%3Athread%3B%0Ause+std%3A%3Atime%3A%3ADuration%3B%0A%0Astruct+JobStatus+%7B%0A++++jobs_completed%3A+u32%2C%0A%7D%0A%0Afn+main%28%29+%7B%0A++++let+status+%3D+Arc%3A%3Anew%28JobStatus+%7B+jobs_completed%3A+0+%7D%29%3B%0A++++let+status_shared+%3D+status.clone%28%29%3B%0A++++thread%3A%3Aspawn%28move+%7C%7C+%7B%0A++++++++for+_+in+0..10+%7B%0A++++++++++++thread%3A%3Asleep%28Duration%3A%3Afrom_millis%28250%29%29%3B%0A++++++++++++status_shared.jobs_completed+%2B%3D+1%3B%0A++++++++%7D%0A++++%7D%29%3B%0A++++while+status.jobs_completed+%3C+10+%7B%0A++++++++println%21%28%22waiting...+%22%29%3B%0A++++++++thread%3A%3Asleep%28Duration%3A%3Afrom_millis%28500%29%29%3B%0A++++%7D%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+%60Arc%60+is+an+Atomic+Reference+Counted+pointer+that+allows+safe%2C+shared+access%0A%2F%2F+to+**immutable**+data.+But+we+want+to+*change*+the+number+of+%60jobs_completed%60%0A%2F%2F+so+we%27ll+need+to+also+use+another+type+that+will+only+allow+one+thread+to%0A%2F%2F+mutate+the+data+at+a+time.+Take+a+look+at+this+section+of+the+book%3A%0A%2F%2F+https%3A%2F%2Fdoc.rust-lang.org%2Fstable%2Fbook%2Fsecond-edition%2Fch16-03-shared-state.html%23atomic-reference-counting-with-arct%0A%2F%2F+and+keep+scrolling+if+you%27d+like+more+hints+%3A%29%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Do+you+now+have+an+%60Arc%60+%60Mutex%60+%60JobStatus%60+at+the+beginning+of+main%3F+Like%3A%0A%2F%2F+%60let+status+%3D+Arc%3A%3Anew%28Mutex%3A%3Anew%28JobStatus+%7B+jobs_completed%3A+0+%7D%29%29%3B%60%0A%2F%2F+Similar+to+the+code+in+the+example+in+the+book+that+happens+after+the+text%0A%2F%2F+that+says+%22We+can+use+Arc%3CT%3E+to+fix+this.%22.+If+not%2C+give+that+a+try%21+If+you%0A%2F%2F+do+and+would+like+more+hints%2C+keep+scrolling%21%21%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+Make+sure+neither+of+your+threads+are+holding+onto+the+lock+of+the+mutex%0A%2F%2F+while+they+are+sleeping%2C+since+this+will+prevent+the+other+thread+from%0A%2F%2F+being+allowed+to+get+the+lock.+Locks+are+automatically+released+when%0A%2F%2F+they+go+out+of+scope.%0A%0A%2F%2F+Ok%2C+so%2C+real+talk%2C+this+was+actually+tricky+for+*me*+to+do+too.+And%0A%2F%2F+I+could+see+a+lot+of+different+problems+you+might+run+into%2C+so+at+this%0A%2F%2F+point+I%27m+not+sure+which+one+you%27ve+hit+%3A%29+Please+see+a+few+possible%0A%2F%2F+answers+on+https%3A%2F%2Fgithub.com%2Fcarols10cents%2Frustlings%2Fissues%2F3+--%0A%2F%2F+mine+is+a+little+more+complicated+because+I+decided+I+wanted+to+see%0A%2F%2F+the+number+of+jobs+currently+done+when+I+was+checking+the+status.%0A%0A%2F%2F+Please+open+an+issue+if+you%27re+still+running+into+a+problem+that%0A%2F%2F+these+hints+are+not+helping+you+with%2C+or+if+you%27ve+looked+at+the+sample%0A%2F%2F+answers+and+don%27t+understand+why+they+work+and+yours+doesn%27t.%0A%0A%2F%2F+If+you%27ve+learned+from+the+sample+solutions%2C+I+encourage+you+to+come%0A%2F%2F+back+to+this+exercise+and+try+it+again+in+a+few+days+to+reinforce%0A%2F%2F+what+you%27ve+learned+%3A%29%0A)
 
 ### Uncategorized