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";

...

struct bignum
{
	ulong[] data;

	...
	
	void opAssign(char[] value)()
	{
		data = toBigInt!(value);
	}
}

or something like that.  BigNums come to mind as a simple example, but I've run into this sort of thing other times too.  Hard to put it down since I don't know if it's even possible, much less what it would look like.

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.

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.

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.