The state of string interpolation

[Adam D. Ruppe]

On Saturday, 8 December 2018 at 02:49:46 UTC, H. S. Teoh wrote:
> Hmph.  I forgot about this limitation of compile-time tuples 
> aka AliasSeq: you cannot capture expressions this way. :-(

The problem with AliasSeq!() is the !() part - it is passing them 
as compile-time arguments, and thus it must be available at 
compile time *for the template it is being passed to*.

But the compiler itself has no such limitation. And as proof, 
consider std.traits.Parameters. You can set items in that to 
runtime values and pass them to functions... just not *templates* 
because the variables a+b need to be available.

Also, struct.tupleof works fine. We aren't capturing expressions 
per se, we are capturing the values of those evaluating those 
expressions. Passing it to a compile time thing would complain, 
but passing it to a runtime function would be fine, just like how

Template!(a+b)

only works if they can be CTFE'd, whereas

Function(a+b)

is totally fine