Do you remember how, in Cairo 0, there was no concise way how to update a struct? We had to write out all its members even if only one changed. It was pretty annoying, as RoboTeddy pointed out in his now legendary post.
Cairo 1 fixes that. By declaring a struct as mutable it becomes possible to assign new values to any member of said struct:
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struct Point {
x: u64,
y: u64,
z: u64
}
let mut place = Point { x: 0, y: 42, z: 69 };
place.x = 33; // Point { x: 33, y: 42, z: 69 }
Easy and kinda obvious, isn’t it? h/t to bllu for teaching me this.