void main()
{
    import std.math : abs, sgn;

    alias n_type = short; //or int, long, byte, whatever

    assert(n_type.min == abs(n_type.min));
    assert(sgn(abs(n_type.min)) == -1);
}

I stumbled into this fun today. I understand why abs yields a negative value here with overflow and no promotion. I just want to know if it should. Should abs ever return a negative number? Thanks.

On Thursday, 28 October 2021 at 21:23:15 UTC, kyle wrote:

void main()
{
    import std.math : abs, sgn;

    alias n_type = short; //or int, long, byte, whatever

    assert(n_type.min == abs(n_type.min));
    assert(sgn(abs(n_type.min)) == -1);
}

Okay I checked the phobos docs and it does say "Limitations
Does not work correctly for signed intergal types and value Num.min." Should have looked there first, I know. Still seems pretty silly.

On Thursday, 28 October 2021 at 21:26:04 UTC, kyle wrote:

I recommend to implement your own abs function this way (was not accepted for phobos, as it now does NOT return the same type as the argument, which was considered a "breaking change" :-( ):

/// get the absolute value of x as unsigned type. always succeeds, even for T.min
Unsigned!T abs(T)(const(T) x) if(isIntegral!T)
{
   static if(isSigned!T) if(x < 0) return cast(Unsigned!T)-x;
   return x;
}

On Thursday, 28 October 2021 at 21:23:15 UTC, kyle wrote:

void main()
{
    import std.math : abs, sgn;

    alias n_type = short; //or int, long, byte, whatever

    assert(n_type.min == abs(n_type.min));
    assert(sgn(abs(n_type.min)) == -1);
}

Depends on how you view it. Imo abs should never be able to return a negative value since it should be the distance/length from 0 and alternaticely root of x^2 .

On Friday, 29 October 2021 at 08:33:07 UTC, Imperatorn wrote:

Yes, but phobos defines it to return a signed type, so theoretical it can return negative values. And they won't change that.

I really think it should return an unsigned type, but that's a "breaking change".
Bullshit policy!

On Friday, 29 October 2021 at 09:35:09 UTC, Dom DiSc wrote:

Eeh... Why does it return unsigned in phobos? Is it just to stay compatible with C? 🤔

Unsigned integers aren't numbers.
assert(-abs(1)<0);

On Friday, 29 October 2021 at 14:23:49 UTC, Kagamin wrote:

That's what I mean. The mapping between number classes and data types are too vague.

On Friday, 29 October 2021 at 14:23:49 UTC, Kagamin wrote:

Unsigneds approximate whole numbers of course (truncated on one side). Likewise signeds approximate integers (across a restricted interval). As always, we need to be careful with approximations.