Saturating<T> wrapper type

[m4rw3r]

Rust's stdlib has a Wrapping<T> wrapper type for primitive integer types. The type provides intentionally wrapping semantics to all operations performed on it.

This pull-request introduces a Saturating<T> wrapper type which is the corresponding saturating wrapper type for primitive integer types. This type provides saturating semantics on arithmetic and bit-shifting operations for both signed and unsigned integers.

The goal is to provide a type which is easy to slot in instead of either Wrapping<T> or any basic integer type. Combined with the traits in num it would be possible to make functions/methods generic over the type of integer and if it should have wrapping or saturating semantics.

The name Saturating<T> collides with the trait Saturating which is unfortunate. I suspect that this type will need a name change but at the moment I do not have any suggestions.

[SoniEx2]

Uh this doesn't look right...

[m4rw3r]

Oops

[cuviper]

Saturating<T> was also just suggested for the standard library in rust-lang/rfcs#1218 (comment). It's a reasonable idea, but don't you think it would make more sense implemented next to Wrapping<T>?

I'm not sure that I agree that implementing num traits for this is helpful. Notice we have nothing yet implemented for Wrapping<T> either. I feel like it would be surprising for a generic function taking Num to encounter wrapping or saturating semantics. Can you give a concrete example where this would really be useful to you?

[m4rw3r]

@cuviper I guess it depends on the number of people who think it would be useful, but it does make more sense to provide both Wrapping<T>, Saturating<T> and maybe even some Checked<T> (always panic on overflow) in the standard library.

As for usefulness in the generic case I have some code which is read from external input where I do not mind if the values are saturated if they are out of bounds, here it is useful with a saturating datatype since I do not have to manually perform checks to make sure that the data I read is within the range of the datatype.

[SoniEx2]

Would be nice to have traits for wrapping_add(), saturating_add(), etc, and have a Wrapping, Saturating, etc impl for them. But that's another issue.

[cuviper]

@m4rw3r then will you propose this for the standard library instead?
If that's rejected, then we can reconsider it here...

[m4rw3r]

@cuviper Submitted as an RFC here: rust-lang/rfcs#1534 this also includes the always-checked counterpart too.

[homu]

☔ The latest upstream changes (presumably #164) made this pull request unmergeable. Please resolve the merge conflicts.

[cuviper]

If this is ever revived, it will need to be on the separate repo:
https://github.com/rust-num/num-traits