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submitted 6 months ago by SorteKanin@feddit.dk to c/rust@programming.dev

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[–] kevincox@lemmy.ml 6 points 6 months ago (4 children)

This is a nice small feature. I'm curious about the commit description:

foo(const { 1 + 1 })

which is roughly desugared into

struct Foo;
impl Foo {
    const FOO: i32 = 1 + 1;
}
foo(Foo::FOO)

I would have expected it to desugar to something like:

foo({
  const TMP: i32 = 1 + 1;
  TMP
})

But I can't seem an explanation why the struct with impl is used. I wonder if it has something to do with propagating generics.

[–] 0v0@sopuli.xyz 10 points 6 months ago (2 children)

It's because it has to work in pattern contexts as well, which are not expressions.

[–] SorteKanin@feddit.dk 2 points 6 months ago (1 children)

Wait, in pattern context? How? Can you give an example?

[–] 0v0@sopuli.xyz 10 points 6 months ago

fn foo(x: i32) {
    match x {
        const { 3.pow(3) } => println!("three cubed"),
        _ => {}
    }
}

But it looks like inline_const_pat is still unstable, only inline_const in expression position is now stabilized.

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