core::raw_mut - Rust
Description: API documentation for the Rust `raw_mut` macro in crate `core`.
Keywords: rust, rustlang, rust-lang, raw_mut

# [−][src]Macro core::raw_mut

    pub macro raw_mut($e:expr) {
        ...
    }

🔬 This is a nightly-only experimental API. (`raw_ref_macros` #73394)

Create a `mut` raw pointer to a place, without creating an intermediate reference.

Creating a reference with `&`/`&mut` is only allowed if the pointer is properly aligned and points to initialized data. For cases where those requirements do not hold, raw pointers should be used instead. However, `&mut expr as *mut _` creates a reference before casting it to a raw pointer, and that reference is subject to the same rules as all other references. This macro can create a raw pointer without creating a reference first.

# Example

    #![feature(raw_ref_macros)]
    use std::ptr;

    #[repr(packed)]
    struct Packed {
        f1: u8,
        f2: u16,
    }

    let mut packed = Packed { f1: 1, f2: 2 };
    // `&mut packed.f2` would create an unaligned reference, and thus be Undefined Behavior!
    let raw_f2 = ptr::raw_mut!(packed.f2);
    unsafe { raw_f2.write_unaligned(42); }
    assert_eq!({packed.f2}, 42); // `{...}` forces copying the field instead of creating a reference.

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