consider const panic if min > max

[dzmitry-lahoda]

bounded-vec/src/bounded_vec.rs

Line 14 in 8265180

// Assert<{ L > 0 }>: IsTrue,

that compiles for me:

#[allow(non_snake_case)]
pub trait RC5<Word, const WS: usize, const R: u8, const B: u8>
where
    Word: Sized
        + WrappingShl<Output = Word>
        + WrappingShr<Output = Word>
        + BitAnd<Output = Word>
        + Add<Output = Word>
        + BitOr<Word, Output = Word>
        + WrappingAdd
        + Copy
        + LeBytes<WS>
        + BitXor<Output = Word>
        + From<u8>
        + Zero,
{
    const W_BYTES: u8 = if std::mem::size_of::<Word>() > WS || Self::R < Self::B  {
        panic!("Word size must be WS")
    } else {
        WS as u8
    };

[greenhat]

Thank you for this idea! I tried this on stable (1.63):

trait CheckBounds<const L: usize, const U: usize> {
    const WB: u8 = if Self::L > Self::U || Self::L == 0 {
        panic!("invalid bounds")
    } else {
        1
    };
}

impl<T, const L: usize, const U: usize> CheckBounds<L, U> for BoundedVec<T, L, U> {}

and got:

error[E0599]: no associated item named `L` found for type parameter `Self` in the current scope
  --> src/bounded_vec.rs:47:29
   |
47 |     const WB: u8 = if Self::L > Self::U || Self::L == 0 {
   |                             ^ associated item not found in `Self`

error[E0599]: no associated item named `U` found for type parameter `Self` in the current scope
  --> src/bounded_vec.rs:47:39
   |
47 |     const WB: u8 = if Self::L > Self::U || Self::L == 0 {
   |                                       ^ associated item not found in `Self`

error[E0599]: no associated item named `L` found for type parameter `Self` in the current scope
  --> src/bounded_vec.rs:47:50
   |
47 |     const WB: u8 = if Self::L > Self::U || Self::L == 0 {
   |                                                  ^ associated item not found in `Self`

Any ideas? Maybe you're have some features enabled that allow this.

[dzmitry-lahoda]

https://github.com/dzmitry-lahoda-forks/rc5_test/blob/master/src/lib.rs#L13

[greenhat]

Oh, it's #![feature(generic_const_exprs)] that is not available on stable yet. I'm keeping an eye on it and will implement the checks as soon as it gets into stable.

[dzmitry-lahoda]

you may expose in toml
[features]
generic_const_exprs =[]

so

#[cfg(feature(generic_const_exprs))
#[feature(generic_const_exprs)]

so you can have both stable and unstable, unstable with future proof feature

[greenhat]

Good idea! Thank you!