Pre-RFC: User-provided default field values

[scottmcm]

@jhpratt

You know, I was going to ask about why, but then I realized that trying to use a tuple struct or variant would lead to a syntactic ambiguity in that .. is a range expression.

From the previous thread:

Pre-pre-RFC: syntactic sugar for `Default::default()`

Why not just go all the way then #[allow(non_upper_case_globals)] static Foo: FooConstructor = FooConstructor; #[derive(Copy, Clone)] struct FooConstructor; impl FnOnce<(i32, i32, RangeFull)> for FooConstructor { type Output = Foo; extern "rust-call" fn call_once(self, (_0, _1, ..): (i32, i32, RangeFull)) -> Foo { Foo { _0, _1, _2: 4, _3: 5 } } } impl FnOnce<(i32, i32, i32, RangeFull)> for FooConstructor { type Output = Foo; extern "rust-call" fn call_once(self, (…

(More for amusement than a serious proposal for v1 of this. I agree sticking to braced-structs for now makes sense.)