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Higher-Rank Types fail with "use of undeclared identifier" #4828
Description
Consider the function:
pub fn foo(bar: fn (comptime A: type, _: A) A) []u8 {
return bar([]u8, "Hello World!");
}The latter two uses of A will fail with use of undeclared identifier, even though they're perfectly valid to use. A workaround verifies this:
fn foo_bar_type(comptime A: type, _: A) A {}
pub fn foo(bar: @TypeOf(foo_bar_type)) [] u8 {
return bar([]u8, "Hello World!");
}However, said workaround is not able to capture types from previous parameters:
pub fn Monad(
comptime M: fn (comptime _: type) type,
pure0: fn (comptime A: type, _: A) M(A), // How to capture M here?
flat_map0: fn (comptime A: type, comptime B: type, _: M(A), _: fn (_: A) M(B)) M(B)
) type {
return struct {
pub const pure = pure0;
pub const flat_map = flat_map0;
};
}(There's some pseudo-ish code here for testing my usecase)
Activity
tadeokondrak commentedon Sep 17, 2020
Note that using
@TypeOfon function definitions works:Edit: ...but doesn't seem to actually type check the functions against the types correctly.
MVPuccino commentedon Aug 12, 2025
Any updates on this? I've been trying to implement an interface akin to GenericReader/GenericWriter but the lack of "Higher-Rank Types" is quite the road-blocker.