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46 lines
1.2 KiB
Rust
46 lines
1.2 KiB
Rust
// ./src/scope/borrow.md
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// This function takes ownership of a box and destroys it
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fn eat_box_i32(boxed_i32: Box<i32>) {
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println!("Destroying box that contains {}", boxed_i32);
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}
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// This function borrows an i32
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fn borrow_i32(borrowed_i32: &i32) {
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println!("This int is: {}", borrowed_i32);
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}
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fn part0() {
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// Create a boxed i32, and a stacked i32
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let boxed_i32 = Box::new(5_i32);
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let stacked_i32 = 6_i32;
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// Borrow the contents of the box. Ownership is not taken,
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// so the contents can be borrowed again.
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borrow_i32(&boxed_i32);
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borrow_i32(&stacked_i32);
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{
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// Take a reference to the data contained inside the box
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let _ref_to_i32: &i32 = &boxed_i32;
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// Error!
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// Can't destroy `boxed_i32` while the inner value is borrowed later in scope.
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// eat_box_i32(boxed_i32);
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// FIXME ^ Comment out this line
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// Attempt to borrow `_ref_to_i32` after inner value is destroyed
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borrow_i32(_ref_to_i32);
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// `_ref_to_i32` goes out of scope and is no longer borrowed.
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}
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// `boxed_i32` can now give up ownership to `eat_box` and be destroyed
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eat_box_i32(boxed_i32);
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}
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pub fn main() {
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part0();
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}
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