Lazy template arguments?

[bearophile]

monarch_dodra:

> Is this proposal a pure optimization trick, or is there some 
> functionality gains here. The only one I can think of, is if 
> "Foo!B" would fail to compile. Is this what you are going 
> for...?

It's first of all a way to implement a Ternary in library code, 
because in some situations instantiating a template causes an 
error, so the lazyness is needed to avoid those errors, and 
instantiate only the correct branch/argument. If this feature 
also reduces the compilation time a bit, then it's welcome :-)

Beside implementing a Ternary, do you see other usages for such 
lazy template arguments?


> Also:
> //----
> template Ternary(bool b, T1, lazy T2) {
> //----
> While is only T2 lazy?

My mistake, both of those arguments are better to be lazy:

template Ternary(bool b, lazy T1, lazy T2) {...}

Bye,
bearophile