the trait core::convert::From<usize> is not implemented for the type u64 #30495

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1. petrochenkov commented on Dec 20, 2015

   

   petrochenkov

   on Dec 20, 2015

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   I can't find where the other integer From traits are defined.

   https://github.com/rust-lang/rust/blob/master/src/libcore/num/mod.rs#L1984

   The discusion about usize is in #28921 and #29220 (make sure to "Show outdated diff")
   TL;DR: We need more motivating examples and maybe some mini-RFC describing the portability aspect to dispel the fears of the libs team.
2. kornelski commented on Dec 20, 2015

   

   kornelski

   on Dec 20, 2015

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   Thanks @petrochenkov. Both issues are about conversion to usize, which is the opposite direction than specified in this issue. I needed conversion from usize to u64 in order to use a FFI.

   Anyway, I've noticed that there is a trait for usize to size_t, so I can tweak my FFI and use that instead.
3. kornelski

   closed this as completedon Dec 20, 2015