QSelf Call Syntax

Demonstrates direct <T>::method() call syntax on complex (non-ident) self types. Inside a generic function, T::method() resolves via monomorphization (see trait impls). For direct calls where the concrete type is named at the call site, Rust requires the qualified-self form <T>::method() when T is not a simple identifier — e.g. <[u32; 4]>::zero(). The proc-macro mangles the qself type into the same identifier the impl block’s self type produces, so the call resolves to the same Type_method WGSL function.

Rust Source

#![allow(unused)]
fn main() {
#[wgsl]
pub mod qself_call_example {
    pub trait Zeroable {
        fn zero() -> Self;
    }

    impl Zeroable for u32 {
        fn zero() -> u32 {
            0
        }
    }

    impl Zeroable for [u32; 4] {
        fn zero() -> [u32; 4] {
            [0u32, 0u32, 0u32, 0u32]
        }
    }

    /// Direct QSelf call on a scalar — `<u32>::zero()` resolves to
    /// `u32_zero()`.
    pub fn scalar_zero() -> u32 {
        <u32>::zero()
    }

    /// Direct QSelf call on an array — `<[u32; 4]>::zero()` resolves to
    /// `_2array_u32_4_zero()`.
    pub fn array_zero() -> [u32; 4] {
        <[u32; 4]>::zero()
    }
}
}

Generated WGSL

fn u32_zero() -> u32 {
    return 0;
}

fn _2array_u32_4_zero() -> array<u32, 4> {
    return array(0u, 0u, 0u, 0u);
}

fn scalar_zero() -> u32 {
    return u32_zero();
}

fn array_zero() -> array<u32, 4> {
    return _2array_u32_4_zero();
}

Notes

• <u32>::zero() and <[u32; 4]>::zero() resolve to the same mangled functions the impl blocks emit (u32_zero and _2array_u32_4_zero).
• The _2 prefix is the bijective mangled encoding of the array_u32_4 self type.
• Associated constants work too: <Tag>::DEFAULT resolves to Tag_DEFAULT.
• Inside generic functions, QSelf calls on types containing type parameters (<T>::method(), <[T; 4]>::zero(), <Pair<T>>::zero()) are rewritten during monomorphization to the concrete impl’s function.
• The <T as Trait>::method() disambiguation form is rejected with a helpful error — trait impls are matched by self type only.
• Generic (turbofish) arguments on the method after >:: are not supported in the QSelf form.