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[-] kevincox@lemmy.ml 6 points 4 months ago

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 4 months ago

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

[-] SorteKanin@feddit.dk 2 points 4 months ago

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

[-] 0v0@sopuli.xyz 10 points 4 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.

this post was submitted on 25 Apr 2024

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