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Be more specific with what I'm talking about

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Carol (Nichols || Goulding) 2015-09-22 22:22:26 -04:00
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@ -67,7 +67,7 @@ Relevant chapters in the book:
- [Ownership](https://doc.rust-lang.org/stable/book/ownership.html)
- [References and borrowing](https://doc.rust-lang.org/stable/book/references-and-borrowing.html)
Note that they may look similar but they are subtly different :)
Note that the exercises in this section may look similar to each other but they are subtly different :)
- ["move_semantics1.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile%21+Scroll+down+for+hints+%3A%29%0A%0Apub+fn+main%28%29+%7B%0A++++let+vec0+%3D+Vec%3A%3Anew%28%29%3B%0A%0A++++let+vec1+%3D+fill_vec%28vec0%29%3B%0A%0A++++println%21%28%22%7B%7D+has+length+%7B%7D+content+%60%7B%3A%3F%7D%60%22%2C+%22vec1%22%2C+vec1.len%28%29%2C+vec1%29%3B%0A%0A++++vec1.push%2888%29%3B%0A%0A++++println%21%28%22%7B%7D+has+length+%7B%7D+content+%60%7B%3A%3F%7D%60%22%2C+%22vec1%22%2C+vec1.len%28%29%2C+vec1%29%3B%0A%0A%7D%0A%0Afn+fill_vec%28vec%3A+Vec%3Ci32%3E%29+-%3E+Vec%3Ci32%3E+%7B%0A++++let+mut+vec+%3D+vec%3B%0A%0A++++vec.push%2822%29%3B%0A++++vec.push%2844%29%3B%0A++++vec.push%2866%29%3B%0A%0A++++vec%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+So+you%27ve+got+the+%22cannot+borrow+immutable+local+variable+%60vec1%60+as+mutable%22+error+on+line+8%2C%0A%2F%2F+right%3F+The+fix+for+this+is+going+to+be+adding+one+keyword%2C+and+the+addition+is+NOT+on+line+8%0A%2F%2F+where+the+error+is.%0A)
- ["move_semantics2.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile+without+changing+line+9%21+Scroll+down+for+hints+%3A%29%0A%0Apub+fn+main%28%29+%7B%0A++++let+vec0+%3D+Vec%3A%3Anew%28%29%3B%0A%0A++++let+mut+vec1+%3D+fill_vec%28vec0%29%3B%0A%0A++++%2F%2F+Do+not+change+the+following+line%21%0A++++println%21%28%22%7B%7D+has+length+%7B%7D+content+%60%7B%3A%3F%7D%60%22%2C+%22vec0%22%2C+vec0.len%28%29%2C+vec0%29%3B%0A%0A++++vec1.push%2888%29%3B%0A%0A++++println%21%28%22%7B%7D+has+length+%7B%7D+content+%60%7B%3A%3F%7D%60%22%2C+%22vec1%22%2C+vec1.len%28%29%2C+vec1%29%3B%0A%0A%7D%0A%0Afn+fill_vec%28vec%3A+Vec%3Ci32%3E%29+-%3E+Vec%3Ci32%3E+%7B%0A++++let+mut+vec+%3D+vec%3B%0A%0A++++vec.push%2822%29%3B%0A++++vec.push%2844%29%3B%0A++++vec.push%2866%29%3B%0A%0A++++vec%0A%7D%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%0A%2F%2F+So+%60vec0%60+is+being+*moved*+into+the+function+%60fill_vec%60+when+we+call+it+on%0A%2F%2F+line+6%2C+which+means+it+gets+dropped+at+the+end+of+%60fill_vec%60%2C+which+means+we%0A%2F%2F+can%27t+use+%60vec0%60+again+on+line+9+%28or+anywhere+else+in+%60main%60+after+the%0A%2F%2F+%60fill_vec%60+call+for+that+matter%29.+We+could+fix+this+in+a+few+ways%2C+try+them%0A%2F%2F+all%21%0A%2F%2F+1.+Make+another%2C+separate+version+of+the+data+that%27s+in+%60vec0%60+and+pass+that%0A%2F%2F+to+%60fill_vec%60+instead.%0A%2F%2F+2.+Make+%60fill_vec%60+borrow+its+argument+instead+of+taking+ownership+of+it%2C%0A%2F%2F+and+then+copy+the+data+within+the+function+in+order+to+return+an+owned%0A%2F%2F+%60Vec%3Ci32%3E%60%0A%2F%2F+3.+Make+%60fill_vec%60+*mutably*+borrow+its+argument+%28which+will+need+to+be%0A%2F%2F+mutable%29%2C+modify+it+directly%2C+then+not+return+anything.+Then+you+can+get+rid%0A%2F%2F+of+%60vec1%60+entirely+--+note+that+this+will+change+what+gets+printed+by+the%0A%2F%2F+first+%60println%21%60%0A)