Rust by Example

Freezing

When data is bound by the same name immutably, it also freezes. Frozen data can't be modified until the immutable binding goes out of scope:

fn main() {

let mut _mutable_integer = 7i32;

{

// Shadowing by immutable `_mutable_integer`

let _mutable_integer = _mutable_integer;

// Error! `_mutable_integer` is frozen in this scope

_mutable_integer = 50;

// FIXME ^ Comment out this line

// `_mutable_integer` goes out of scope

}

// Ok! `_mutable_integer` is not frozen in this scope

_mutable_integer = 3;

}

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