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# Error code E0799

Something other than a type or const parameter has been used when one was expected.

Erroneous code example:

    fn bad1() -> impl Sized + use<main> {}

    fn bad2(x: ()) -> impl Sized + use<x> {}

    fn main() {}

In the given examples, for `bad1`, the name `main` corresponds to a function rather than a type or const parameter. In `bad2`, the name `x` corresponds to a function argument rather than a type or const parameter.

Only type and const parameters, including `Self`, may be captured by `use<...>` precise capturing bounds.