Incorporate Move Semantics exercises from Felix's tutorial

👍 👍 👍

Connects to #6

README.md

@@ -59,6 +59,20 @@ following exercises will ask you to make tests pass!
 - ["strings2.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile+without+changing+the+function+signature%21+Scroll+down+for+hints+%3A%29%0A%0Afn+main%28%29+%7B%0A++++let+guess1+%3D+%22blue%22.to_string%28%29%3B+%2F%2F+Try+not+changing+this+line+%3A%29%0A++++let+correct+%3D+guess_favorite_color%28guess1%29%3B%0A++++if+correct+%7B%0A++++++++println%21%28%22You+guessed+correctly%21%22%29%3B%0A++++%7D+else+%7B%0A++++++++println%21%28%22Nope%2C+that%27s+not+it.%22%29%3B%0A++++%7D%0A%7D%0A%0Afn+guess_favorite_color%28attempt%3A+%26str%29+-%3E+bool+%7B%0A++++attempt+%3D%3D+%22green%22%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%2F%2F+Yes%2C+it+would+be+really+easy+to+fix+this+by+just+changing+the+value+bound+to+%60guess1%60+to+be+a%0A%2F%2F+string+slice+instead+of+a+%60String%60%2C+wouldn%27t+it%3F%3F+There+is+a+way+to+add+one+character+to+line%0A%2F%2F+5%2C+though%2C+that+will+coerce+the+%60String%60+into+a+string+slice.%0A)
 - ["strings3.rs"](http://play.rust-lang.org/?code=%2F%2F+Ok%2C+here+are+a+bunch+of+values--+some+are+%60Strings%60%2C+some+are+%60%26strs%60.+Your%0A%2F%2F+task+is+to+call+one+of+these+two+functions+on+each+value+depending+on+what%0A%2F%2F+you+think+each+value+is.+That+is%2C+add+either+%60string_slice%60+or+%60string%60%0A%2F%2F+before+the+parentheses+on+each+line.+If+you%27re+right%2C+it+will+compile%21%0A%0Afn+string_slice%28arg%3A+%26str%29+%7B+println%21%28%22%7B%7D%22%2C+arg%29%3B+%7D%0Afn+string%28arg%3A+String%29+%7B+println%21%28%22%7B%7D%22%2C+arg%29%3B+%7D%0A%0Afn+main%28%29+%7B%0A++++%28%22blue%22%29%3B%0A++++%28%22red%22.to_string%28%29%29%3B%0A++++%28String%3A%3Afrom%28%22hi%22%29%29%3B%0A++++%28format%21%28%22Interpolation+%7B%7D%22%2C+%22Station%22%29%29%3B%0A++++%28%26String%3A%3Afrom%28%22abc%22%29%5B0..1%5D%29%3B%0A++++%28%22++hello+there+%22.trim%28%29%29%3B%0A++++%28%22Happy+Monday%21%22.to_string%28%29.replace%28%22Mon%22%2C+%22Tues%22%29%29%3B%0A++++%28%22mY+sHiFt+KeY+iS+sTiCkY%22.to_lowercase%28%29%29%3B%0A%7D%0A)
 
+### Move semantics
+
+These exercises are adapted from [pnkfelix]()'s [Rust Tutorial](http://pnkfelix.github.io/rust-examples-icfp2014/) -- thank you Felix!!!
+
+They may look similar but they are subtly different :)
+
+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)
+
+- ["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)
+- ["move_semantics3.rs"](http://play.rust-lang.org/?code=%2F%2F+Make+me+compile+without+adding+new+lines--+just+changing+existing+lines%21%0A%2F%2F+%28no+lines+with+multiple+semicolons+necessary%21%29%0A%2F%2F+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++++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++++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%0A%0A%2F%2F+The+difference+between+this+one+and+the+previous+ones+is+that+the+first+line%0A%2F%2F+of+%60fn+fill_vec%60+that+had+%60let+mut+vec+%3D+vec%3B%60+is+no+longer+there.+You+can%2C%0A%2F%2F+instead+of+adding+that+line+back%2C+add+%60mut%60+in+one+place+that+will+change%0A%2F%2F+an+existing+binding+to+be+a+mutable+binding+instead+of+an+immutable+one+%3A%29%0A)
+- ["move_semantics4.rs"](http://play.rust-lang.org/?code=%2F%2F+Refactor+this+code+so+that+instead+of+having+%60vec0%60+and+creating+the+vector%0A%2F%2F+in+%60fn+main%60%2C+we+instead+create+it+within+%60fn+fill_vec%60+and+transfer+the%0A%2F%2F+freshly+created+vector+from+fill_vec+to+its+caller.+Scroll+for+hints%21%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++++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%2F%2F+Stop+reading+whenever+you+feel+like+you+have+enough+direction+%3A%29+Or+try%0A%2F%2F+doing+one+step+and+then+fixing+the+compiler+errors+that+result%21%0A%2F%2F+So+the+end+goal+is+to%3A%0A%2F%2F+-+get+rid+of+the+first+line+in+main+that+creates+the+new+vector%0A%2F%2F+-+so+then+%60vec0%60+doesn%27t+exist%2C+so+we+can%27t+pass+it+to+%60fill_vec%60%0A%2F%2F+-+we+don%27t+want+to+pass+anything+to+%60fill_vec%60%2C+so+its+signature+should%0A%2F%2F+++reflect+that+it+does+not+take+any+arguments%0A%2F%2F+-+since+we%27re+not+creating+a+new+vec+in+%60main%60+anymore%2C+we+need+to+create%0A%2F%2F+++a+new+vec+in+%60fill_vec%60%2C+similarly+to+the+way+we+did+in+%60main%60%0A)
 
 ### Modules
 

move_semantics/move_semantics1.rs

@@ -0,0 +1,42 @@
+// Make me compile! Scroll down for hints :)
+
+pub fn main() {
+    let vec0 = Vec::new();
+
+    let vec1 = fill_vec(vec0);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+    vec1.push(88);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+}
+
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+    let mut vec = vec;
+
+    vec.push(22);
+    vec.push(44);
+    vec.push(66);
+
+    vec
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+// So you've got the "cannot borrow immutable local variable `vec1` as mutable" error on line 8,
+// right? The fix for this is going to be adding one keyword, and the addition is NOT on line 8
+// where the error is.

move_semantics/move_semantics2.rs

@@ -0,0 +1,53 @@
+// Make me compile without changing line 9! Scroll down for hints :)
+
+pub fn main() {
+    let vec0 = Vec::new();
+
+    let mut vec1 = fill_vec(vec0);
+
+    // Do not change the following line!
+    println!("{} has length {} content `{:?}`", "vec0", vec0.len(), vec0);
+
+    vec1.push(88);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+}
+
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+    let mut vec = vec;
+
+    vec.push(22);
+    vec.push(44);
+    vec.push(66);
+
+    vec
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+// So `vec0` is being *moved* into the function `fill_vec` when we call it on
+// line 6, which means it gets dropped at the end of `fill_vec`, which means we
+// can't use `vec0` again on line 9 (or anywhere else in `main` after the
+// `fill_vec` call for that matter). We could fix this in a few ways, try them
+// all!
+// 1. Make another, separate version of the data that's in `vec0` and pass that
+// to `fill_vec` instead.
+// 2. Make `fill_vec` borrow its argument instead of taking ownership of it,
+// and then copy the data within the function in order to return an owned
+// `Vec<i32>`
+// 3. Make `fill_vec` *mutably* borrow its argument (which will need to be
+// mutable), modify it directly, then not return anything. Then you can get rid
+// of `vec1` entirely -- note that this will change what gets printed by the
+// first `println!`

move_semantics/move_semantics3.rs

@@ -0,0 +1,45 @@
+// Make me compile without adding new lines-- just changing existing lines!
+// (no lines with multiple semicolons necessary!)
+// Scroll down for hints :)
+
+pub fn main() {
+    let vec0 = Vec::new();
+
+    let mut vec1 = fill_vec(vec0);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+    vec1.push(88);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+}
+
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+    vec.push(22);
+    vec.push(44);
+    vec.push(66);
+
+    vec
+}
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+// The difference between this one and the previous ones is that the first line
+// of `fn fill_vec` that had `let mut vec = vec;` is no longer there. You can,
+// instead of adding that line back, add `mut` in one place that will change
+// an existing binding to be a mutable binding instead of an immutable one :)

move_semantics/move_semantics4.rs

@@ -0,0 +1,47 @@
+// Refactor this code so that instead of having `vec0` and creating the vector
+// in `fn main`, we instead create it within `fn fill_vec` and transfer the
+// freshly created vector from fill_vec to its caller. Scroll for hints!
+
+pub fn main() {
+    let vec0 = Vec::new();
+
+    let mut vec1 = fill_vec(vec0);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+    vec1.push(88);
+
+    println!("{} has length {} content `{:?}`", "vec1", vec1.len(), vec1);
+
+}
+
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+    let mut vec = vec;
+
+    vec.push(22);
+    vec.push(44);
+    vec.push(66);
+
+    vec
+}
+
+
+
+
+
+
+
+
+
+
+
+
+// Stop reading whenever you feel like you have enough direction :) Or try
+// doing one step and then fixing the compiler errors that result!
+// So the end goal is to:
+// - get rid of the first line in main that creates the new vector
+// - so then `vec0` doesn't exist, so we can't pass it to `fill_vec`
+// - we don't want to pass anything to `fill_vec`, so its signature should
+//   reflect that it does not take any arguments
+// - since we're not creating a new vec in `main` anymore, we need to create
+//   a new vec in `fill_vec`, similarly to the way we did in `main`