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From's orphan rules being asymmetric is annoying #19

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scottmcm opened this issue Jul 29, 2019 · 1 comment

scottmcm commented Jul 29, 2019

I can do impl<T> From<T> for NewType<T>, but I can't do impl<T> From<NewType<T>> for T even though I can do impl From<NewType<u32>> for u32.

That leads to unfortunate huge sets of impls like https://docs.rs/simd-trick/0.3.0/simd_trick/struct.Simd.html#impl-From%3CSimd%3C%5Bm64%3B%208%5D%3E%3E

The text was updated successfully, but these errors were encountered:

scottmcm changed the title ~~From being asymmetric is annoying~~ From's orphan rules being asymmetric is annoying

nox commented Jul 29, 2019

Couldn't you do impl Into<T> for NewType<T> though? And thus not have all those impls, given end users are supposed to bound on Into not From?

Ixrec mentioned this issue

A Brief History of Rust's Orphan Rules #1

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