Caching of Template Instantiations

[Marc Schütz via Digitalmars-d-learn]

On Saturday, 17 October 2015 at 07:48:39 UTC, Nordlöw wrote:
> Does DMD cache template instantiations?

Yes, and it's required by the spec:

"Multiple instantiations of a TemplateDeclaration with the same 
TemplateArgumentList all will refer to the same instantiation."
http://dlang.org/template.html

>
> That is, is it preferred to do, for instance, either
>
>     static      if (isIntegral!T && isUnsigned!(T)) {}
>     else static if (isIntegral!T && isSigned!(T)) {}
>
> or
>
>     enum integral = isIntegral!T;
>     static      if (integral && isUnsigned!(T)) {}
>     else static if (integral && isSigned!(T)) {}

It *might* make a little difference if you have thousands of 
instantiations, because for each instantiation the compiler needs 
to check whether it has already instantiated the templation with 
that combination of arguments, but I wouldn't worry about it.