26 lines
758 B
Rust
26 lines
758 B
Rust
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// Test that the NLL `relate_tys` code correctly deduces that a
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// function returning always its first argument can be upcast to one
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// that returns either first or second argument.
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use std::cell::Cell;
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type DoubleCell<A> = Cell<(A, A)>;
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type DoublePair<A> = (A, A);
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fn make_cell<'b>(x: &'b u32) -> Cell<(&'static u32, &'b u32)> {
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panic!()
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}
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fn main() {
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let a: &'static u32 = &22;
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let b = 44;
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// Here we get an error because `DoubleCell<_>` requires the same type
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// on both parts of the `Cell`, and we can't have that.
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let x: DoubleCell<_> = make_cell(&b); //~ ERROR
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// Here we do not get an error because `DoublePair<_>` permits
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// variance on the lifetimes involved.
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let y: DoublePair<_> = make_cell(&b).get();
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}
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