On 2008-11-27 22:34:50 -0500, Andrei Alexandrescu
<[EMAIL PROTECTED]> said:
One question I had is: say polysemy will be at work for integral
arithmetic. Should we provide means in the language for user-defined
polysemous functions? Or is it ok to leave it as compiler magic that
saves redundant casts?
I think that'd be a must. Otherwise how would you define your own
arithmetical types so they work like the built-in ones?
struct ArbitraryPrecisionInt { ... }
ArbitraryPrecisionInt a = ...;
uint b = ...;
auto c = a & b;
c <<= 16;
...
Should't c be of type ArbitraryPresisionInt? And shouldn't the
following work too?
uint d = a & b;
That said, how can a function return a polysemous value at all? Should
the function return a special kind of struct with a sample of every
supported type? That'd be utterly inefficient. Should it return a
custom-made struct with the ability to implicitly cast itself to other
types? That would make the polysemous value propagatable through auto,
and probably less efficient too.
The only way I can see this work correctly is with function overloading
on return type, with a way to specify the default function (for when
the return type is not specified, such as with auto). In the case
above, you'd need something like this:
struct ArbitraryPrecisionInt {
default ArbitraryPrecisionInt opAnd(uint i);
uint opAnd(uint i);
}
--
Michel Fortin
[EMAIL PROTECTED]
http://michelf.com/
