Merge pull request #3618 from Emerentius/master

[Rust/en] minor fixes to string slices and borrow system

rust.html.markdown

@@ -92,10 +92,8 @@ fn main() {
     let s: String = "hello world".to_string();
 
     // A string slice – an immutable view into another string
-    // This is basically an immutable pair of pointers to a string – it doesn’t
-    // actually contain the contents of a string, just a pointer to
-    // the begin and a pointer to the end of a string buffer,
-    // statically allocated or contained in another object (in this case, `s`)
+    // The string buffer can be statically allocated like in a string literal
+    // or contained in another object (in this case, `s`)
     let s_slice: &str = &s;
 
     println!("{} {}", s, s_slice); // hello world hello world
@@ -290,7 +288,7 @@ fn main() {
     // Reference – an immutable pointer that refers to other data
     // When a reference is taken to a value, we say that the value has been ‘borrowed’.
     // While a value is borrowed immutably, it cannot be mutated or moved.
-    // A borrow lasts until the end of the scope it was created in.
+    // A borrow is active until the last use of the borrowing variable.
     let mut var = 4;
     var = 3;
     let ref_var: &i32 = &var;
@@ -299,6 +297,8 @@ fn main() {
     println!("{}", *ref_var);
     // var = 5; // this would not compile because `var` is borrowed
     // *ref_var = 6; // this would not either, because `ref_var` is an immutable reference
+    ref_var; // no-op, but counts as a use and keeps the borrow active
+    var = 2; // ref_var is no longer used after the line above, so the borrow has ended
 
     // Mutable reference
     // While a value is mutably borrowed, it cannot be accessed at all.
@@ -309,6 +309,7 @@ fn main() {
     println!("{}", *ref_var2); // 6 , // var2 would not compile.
     // ref_var2 is of type &mut i32, so stores a reference to an i32, not the value.
     // var2 = 2; // this would not compile because `var2` is borrowed.
+    ref_var2; // no-op, but counts as a use and keeps the borrow active until here
 }
 ```