Expand wrap_pyfunction!() to a closure to improve deduction. #1597
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The change to wrap_pyfunction!() in PyO3#1143 makes it impossible to implement `context.add_wrapped(wrap_pyfunction!(something))` in `inline-python`. `context` does not carry the GIL lifetime, which causes type deduction trouble now that `wrap_pyfunction` results in a generic function. ``` error[E0308]: mismatched types --> examples/rust-fn.rs:12:4 | 12 | c.add_wrapped(wrap_pyfunction!(rust_print)); | ^^^^^^^^^^^ one type is more general than the other | = note: expected enum `Result<&pyo3::types::PyCFunction, _>` found enum `Result<&pyo3::types::PyCFunction, _>` ``` By re-wrapping the function as a closure, we trigger 'closure signature deduction' when passing `wrap_pyfunction!()` as an argument to a function: Rustc will deduce the signature of the closure from the function that closure is passed to. This way, the generic arguments can be deduced in more contexts, fixing the problem.
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davidhewitt
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May 6, 2021
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This changes
wrap_pyfunction!()to expand to a closure, to improve deduction when passed to a function without the GIL lifetime.The change to wrap_pyfunction!() in #1143 makes it impossible to implement
context.add_wrapped(wrap_pyfunction!(something))ininline-python.contextdoes not carry the GIL lifetime, which causes type deduction trouble now thatwrap_pyfunctionresults in a generic function.By re-wrapping the function as a closure, we trigger closure signature deduction instead of the regular deduction rules when passing
wrap_pyfunction!()as an argument to a function: Rustc will deduce the signature of the closure from the bounds of the function that closure is passed to. This way, the generic arguments can be deduced in more contexts, fixing the problem.