Remove floating point modulus as a built-in operation; relegate it to the libraries

[brson]

Floating point modulus is rarely used, doesn't exist in C, and is always lowered to an fmod library call. LLVM is considering removing support entirely. Nominating.

[thestinger]

I don't think it should be removed if it can be well-defined and is sometimes useful. The modulus operator can be overloaded in a library anyway, so whether or not it's built-in to the compiler only changes constant evaluation since CTFE isn't part of Rust.

[pcwalton]

I highly doubt anyone will notice it gone. I don't think we should be making design decisions to keep obscure features based on CTFE concerns. For example, sqrt is far more useful than fmod; do we want to build sqrt into the language too so that constants can use it?

[thestinger]

I don't care whether or not it's built-in to the language. I just don't want it completely removed as the bessel functions were. It's absolutely trivial to support it and the API design is very clear cut.

[huonw]

I'd like to at least have the operator overloaded by the traits even if it's not directly in the compiler, e.g. Python offers it

>>> 1.5 % 0.4
0.29999999999999993

[pnkfelix]

Accepted for P-backcompat-lang, 1.0.