IFTI with constant args, is this already possible?
Don Clugston
dac at nospam.com.au
Thu Feb 1 03:04:13 PST 2007
Chad J wrote:
> Don Clugston wrote:
>> Chad J wrote:
>>
>>> So suppose I have a function template, one that is supposed to be
>>> instantiated via IFTI. Then, the user supplies an argument that is
>>> constant (ex: foo(42,"cat")). Is there any way that I can grab those
>>> constant arguments at compile time and use them to do compile time
>>> computation? Even better, can I do it in variadic templates?
>>>
>>> I'm envisioning a situation like this:
>>>
>>> // the string-to-integer conversion is done at compile time
>>> bignum bigAssInteger = "3420894398526094609987620490236001914309690234";
>>
>>
>> There's no syntax sugar for this at present. (Though I've proposed it,
>> and there are indications that it will happen).
>> But:
>>
>> bigAssInteger =
>> toBigInt!("3420894398526094609987620490236001914309690234");
>>
>> is currently possible.
>>
>> Until we get early discard of templates, it's not really a good idea
>> right now because compilation is slow while the compiler generates an
>> enormous obj file full of junk.
>
> Ah. Thanks for the info.
BTW, my proposal was for something like:
BigInt opAssign(super T : char [])(T s){
static if (is(s == const)) {
// compile-time assign
setFromLiteral!(s);
} else {
// runtime-assign.
...
}
}
Requires (1) super in a template parameter list distinguishes between
storage classes.
(2) is( A B == const) --> if A is a literal, sets B to be that literal.
Andrei's storageof() proposal could probably achieve the same thing.
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