[estebank]

> By default Rust's release builds give the integer overflows wrapping, so (1u8 + 255u8 == 0u8) rather than panic, so as to avoid paying for the checks.

I consider that to have been a mistake, and hopefully one we can change. Note that this is about defaults, you can build your own project as release with overflow panics. I'd wish the language had a mechanism to select the math overflow behavior in a more granular way that can be propagated to called functions (in effect, I want integer effects) instead of relying exclusively in the type system:

    fn bar(a: i32, b: i32) -> i32 where i32 is Saturating {
        a + b
    }
    
    fn foo(a: i32, b: i32) -> i32 where i32 is Wrapping {
        // the `a + b` wraps on overflow, but the call to
        // bar overrides the effect of the current function
        // and will saturate instead.
        a + b + bar(a, b)
    }

With this crates can provide control to their callers on math overflow behavior without having to provide type parameters in every API with a bounds for something like https://docs.rs/num-traits/0.2.19/num_traits/.

[tialaramex]

When you say it's a mistake (in your opinion) do you mean that you'd have picked panic in release builds by default? Or do you think Rust 1.0 without full blown effects was the mistake and so you'd actually want effects here and no smaller change is worthwhile ?

Personally I'm not as bothered about this as I was initially, whereas I'm at least as annoyed today by some 'as' casts as I was when I learned Rust -- if I could have your integer effects or abolish narrowing 'as' then I'd abolish narrowing 'as' in a heartbeat. Let people explicitly say what they meant, if I have a u16 and I try to put that in a u8, it will not fit, make me write the fallible conversion and say what happens when it fails. This strikes me as especially hazardous for inferred casts. foo as _ could do more or less anything, it is easily possible that it does something I hadn't considered and will regret, make me write what I meant and we'll avoid that.

[estebank]

The former. Effects is not something that should have blocked 1.0 at all, that was the right call. Don't think it was even on the table back then.

[tialaramex]

Oh, I think I'm onboard with this (default release builds to panic on overflow), for whatever that's worth.