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Rust

Rust

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Using std::mem::size_of_val() on reference of type rather than type itself RS-W1123

Bug risk
Major

Calling std::mem::size_of_val() with a reference to a reference returns the size of the reference type rather than the value pointed to by the reference. This can introduce bugs due to size mismatch in further usage of the calculated value.

Bad practice

struct Foo {
    buffer: &[u8],
}

impl Foo {
    fn size(&self) -> usize {
        // As the `self` argument is already a reference,
        // using `&self` yields a double reference `&&Foo`.
        // Hence, the return value of `size_of_val()` is the
        // size of the reference-type, not the size of `self`.
        std::mem::size_of_val(&self)
    }
}

Recommended

struct Foo {
    buffer: &[u8],
}

impl Foo {
    fn size(&self) -> usize {
        // `self` is `&Foo`, hence the function returns
        // the size of `Foo` pointed to by `self`.
        std::mem::size_of_val(self)
    }
}