Positive

[Bruce Adams]

On Sun, 05 Oct 2008 11:18:24 +0100, KennyTM~ <kennytm at gmail.com> wrote:
>
> Probably they'd used (0, +∞) and [0, +∞) instead.
>
> ---
>
> BTW, negative real numbers can also be indicated as ℝ⁻ (R^- if Unicode  
> is not supported). Is it now special enough to deserve a Negative!()  
> template? :p

Nice use of unicode.

>
> I think these sign checking should be done through contracts or  
> "conditional template" (? whatever it's called; I haven't used one of  
> these yet) instead. Unless you can runtime check that
>
>    Positive!(double) x = 6;
>    Positive!(double) y = 12;

Compile time check

>    Positive!(double) z = void;

This must be an syntax error surely?

>    z = x - y;  // raises error.

The return type of subtraction goes outside the postive domain:
i.e. if it needed to exist (which it probably doesn't) the function spec  
would be:

double opMinus(Positive!(double) y, Positive!(double) y);


So this is actually:

z = cast(Positive!(double))(x - y)

Hence there is the necessary check which could be either run-time or  
compile time.


>    Positive!(double) w;
>    din.readf("%g", &w);  // raises error if user enters negative number.
>
> But I don't think uint, etc now even do these checks.

This would ideally work as above but I see your problem.
The contract of readf is not tight enough. You should rewrite as:

double wtemp;
din.read("%g", &wtemp);
Positive!(double) w = wtemp;    // type check applied here








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