Casts and conversions done right

[Daniel Keep]

Lars T. Kyllingstad wrote:
> Daniel Keep wrote:
>>
>> ...
>>
>> We could probably write another template called reinterpret!T or
>> recast!T or something that explicitly takes a collection of bits and
>> reinterprets them as another type (ie: the *cast(int*)&pi case).
> 
> Wouldn't this by necessity have to be a built-in feature of the language?

Why would it?

ref T recast(T,U)(ref U v) if( T.sizeof <= U.sizeof )
{
    return *cast(T*)&v;
}

Or something similar should be possible.

>> ...
>>
>> As for people wanting to control the rounding mode, etc., that's what
>> functions are for.  My personal position is that stuff like to!T should
>> exist to do perform a sane default conversion; if you want more control,
>> you should use a more specialised function.
> 
> Recently, Julien Leclercq posted an enhancement request for Phobos
> entitled "'std.conv.to': check for a custom 'to' method in
> classes/structs".
> 
>     http://d.puremagic.com/issues/show_bug.cgi?id=3189

Tango already does this.  Actually, it goes a few better than that: any
user-defined type can have to(T), to_{type_name} or to{TypeName} members
that it will use to do conversions as well as static from(T),
from_{type_name} or from{TypeName} methods to do reverse conversions.

> I think it would be a very good idea to make to!(T) *the* convention for
> built-in, standard library and user types. It would make for a unified,
> consistent approach to conversions:
> 
>     double x = 3.14;
>     MyFloat y = 2.72;
> 
>     int i = to!int(x);
>     int j = to!int(y);
>     string s = to!string(x);
>     string t = to!string(y);
> 
> Beautiful, no? :)
> 
> -Lars

Again; why do you think I wrote Tango's to(T) template in the first
place?  :D