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This is still not a conflicting requirement. Rust relies on implicit bounds, that is said in the linked document, and the "universal" quantification there is no

This is still not a conflicting requirement. Rust relies on implicit bounds, that is said in the linked document, and the "universal" quantification there is not really universal, it in fact has a requirement. It's not present in the syntax, but it's present in the type system. The algorithm in the compiler loses that requirement and fails to reject invalid programs. Rust has many cases when it introduces implicit type-level properties, another one is async-fns with its lifetimes and marker-traits such as Send.

nicklecompte 3y ago
> It's not present in the syntax, but it's present in the type system. The trickiness of the bug is that the design of contravariance means the constraint is actually not present in the type system even though it should be. See this other comment I wrote: https://news.ycombinator.com/item?id=39448909 https://news.ycombinator.com/item?id=39448909