Rust memory management: Difference between revisions
From wikinotes
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print_str(s); // `s` does not have `Copy` trait, pointer passed to function, which now owns it | print_str(s); // `s` does not have `Copy` trait, pointer passed to function, which now owns it | ||
println!("{}", s); // <-- BANG! not allowed to use `s` anymore | println!("{}", s); // <-- BANG! not allowed to use `s` anymore | ||
} | |||
</syntaxhighlight> | |||
Passing references enables passing objects to arguments without transferring ownership | |||
<syntaxhighlight lang="rust"> | |||
fn print_str(s: &String) { println!("{}", s); } | |||
fn main() { | |||
let s = String::from("abc"); | |||
print_str(&s); | |||
println!("{}", s); // <<-- valid! `main` still owns the object | |||
} | } | ||
</syntaxhighlight> | </syntaxhighlight> | ||
</blockquote><!-- Ownership --> | </blockquote><!-- Ownership --> | ||
</blockquote><!-- General --> | </blockquote><!-- General --> |
Revision as of 17:19, 7 February 2023
Rust uses ownership semantics for memory management.
Documentation
official tutorial https://doc.rust-lang.org/stable/book/ch04-00-understanding-ownership.html
General
Stack
The stack is
- a LIFO
- push=add, pop=remove (from the top)
- only supports fixed-size datatypes
- fast
Heap
- access provided through pointers (a fixed-size, usable on stack)
- slower
Ownership
- Objects have a single owner at once
- When owner goes out of scope, value is dropped (with
drop()
)- When an object is passed as a function-parameter, that function now owns it (and it cannot be referenced in current context).
See example of ownership in action.
fn print_i32(i: i32) { println!("{}", i); } fn print_str(s: String) { println!("{}", s); } fn main() { let i = 123; print_i32(i); // `i` has `Copy` trait, `foo` gets a shallow copy println!("{}", i); // valid! `i` is still owned by `main()` let s = String::from("abc"); print_str(s); // `s` does not have `Copy` trait, pointer passed to function, which now owns it println!("{}", s); // <-- BANG! not allowed to use `s` anymore }Passing references enables passing objects to arguments without transferring ownership
fn print_str(s: &String) { println!("{}", s); } fn main() { let s = String::from("abc"); print_str(&s); println!("{}", s); // <<-- valid! `main` still owns the object }