T.zero and T.one for numeric types

[w0rp via Digitalmars-d]

On Friday, 17 April 2015 at 13:27:19 UTC, Biotronic wrote:
> I've been writing a lot of generic code lately that has to deal 
> with various kinds of numbers, and have near been driven nuts 
> by the fact there is no uniform way to get a zero or one.
>
> Consider:
>
>    void foo(T)(T a) {}
>
>    foo!T(0);
>
> Does this work with all built-in numeric types? Yes.
> Does it work with T=BigInt or Complex!float? No.
>
> Now, those are a limited set of possibilities, and one could 
> easily enough create a template such that
>
>    foo!BigInt(zero!BigInt);
>
> would work. But why can't I instead, for every numeric type, 
> simply write
>
>    foo(BigInt.zero);
>    foo(float.one);
>    foo(Complex!float.zero);
>    foo(Rational!BigInt.one);
>    foo(Meters.zero);
>
> ?
>
> This would also work for strong typedefs and units of 
> measurement, where simply assigning 0 to a variable might not 
> work (because it lacks the correct unit).
>
> It's a very simple change, both in the compiler and Phobos, and 
> I could have a pull request ready tomorrow.
>
> --
>   Simen

This can be implemented via a library without requiring any 
changes to the language. It would look like Zero!T or One!T 
instead. You create a value template for it.

When you are writing less generic code, you can commit to zero or 
one in certain types via the prefixes. 1L, 1, 1.0, 1.0f. There's 
nothing for short or byte, but you can do short(1), byte(1). You 
can also write T(1) or T(0) to get a numeric type T with the 
value 0 or 1. That might be better than a template, I haven't 
tried it.