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Merge pull request #3618 from Emerentius/master

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[Rust/en] minor fixes to string slices and borrow system
This commit is contained in:
Divay Prakash
2019-09-17 19:24:29 +05:30
committed by GitHub
parent ffb9c5f909 fdd278fde1
commit 69e1b56672
1 changed files with 6 additions and 5 deletions
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rust.html.markdown
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@@ -92,10 +92,8 @@ fn main() {
let s: String = "hello world".to_string(); let s: String = "hello world".to_string();
// A string slice – an immutable view into another string // A string slice – an immutable view into another string
// This is basically an immutable pair of pointers to a string – it doesn’t // The string buffer can be statically allocated like in a string literal
// actually contain the contents of a string, just a pointer to // or contained in another object (in this case, `s`)
// the begin and a pointer to the end of a string buffer,
// statically allocated or contained in another object (in this case, `s`)
let s_slice: &str = &s; let s_slice: &str = &s;
println!("{} {}", s, s_slice); // hello world hello world println!("{} {}", s, s_slice); // hello world hello world
@@ -290,7 +288,7 @@ fn main() {
// Reference – an immutable pointer that refers to other data // 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’. // 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. // 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; let mut var = 4;
var = 3; var = 3;
let ref_var: &i32 = &var; let ref_var: &i32 = &var;
@@ -299,6 +297,8 @@ fn main() {
println!("{}", *ref_var); println!("{}", *ref_var);
// var = 5; // this would not compile because `var` is borrowed // 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 = 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 // Mutable reference
// While a value is mutably borrowed, it cannot be accessed at all. // 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. 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. // 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. // 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
} }
``` ```