Trait for Upcasting / Widening about num HOT 7 CLOSED

I think std::convert::From is the right trait for lossless conversions. But we can't implement that in num except for our own types, like for BigInt/BigUint in #117. Maybe you should propose adding primitive From impls in rust proper?

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BTW, nice graph!

You might simplify it a bit by leaving it implicit for transitive conversions. That is, if A->B and B->C, then implicitly A->C. Hmm, I wonder if a generic impl can express that, something like:

impl<A, B: From<A>, C: From<B>> From<A> for C {
    fn from(a: A) -> C { C::from(B::from(a)) }
}

But the existence of impl<T> From<T> for T might make this explode...

(don't mind me, just musing...)

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Maybe the conv crate covers this appropriately now.

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Does conv have any new infallible conversions? I only see ConvUtil::into_as which is using the standard Into trait anyway.

But I noticed nightly From does now document integer upcasts -- this was merged only 2 days ago in rust-lang/rust#28921! So if you submit a similar addition for floats, you'll be done here. (If you don't want to, let me know and maybe I'll try it.)

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Nice! I had missed that. Please do if you want to!

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The float conversions are now merged! I think there's nothing else to do here.

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Nice!

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