Always false float comparisons

[Ola Fosheim Grøstad via Digitalmars-d]

On Monday, 16 May 2016 at 07:54:32 UTC, Iain Buclaw wrote:
> On 16 May 2016 at 09:22, Ola Fosheim Grøstad via Digitalmars-d 
> <digitalmars-d at puremagic.com> wrote:
>> On Monday, 16 May 2016 at 06:34:04 UTC, Iain Buclaw wrote:
>>
>> No, promoting to double is ok.
>
> Your own example:
>
> const float value = 1.30;
> float  copy = value;
> assert(value*0.5 ==  copy*0.5);
>
> Versus how you'd expect it to work.
>
> const float value = 1.30;
> float  copy = value;
> assert(cast(float)(value*0.5) ==  cast(float)(copy*0.5)); // 
> Compare
> as float, not double.

Promoting to double is sound. That is not the issue. Just replace 
the assert with a function like "check(real x, real y)".  The 
programmer shouldn't have to look it up. Using "check(real x, 
real y)" should _not_ give a different result than using 
"check(float x, float y)". If you have implemented the former, 
you shouldn't have to implement the latter to get reasonable 
results.

Binding to "const float" or "float" should not change the outcome.

The problem is not the promotion, the problem is that you don't 
get the coercion to 32 bit floats where you requested it. This 
violates the principle of "least surprise".