On Wed, 11 Apr 2012 07:42:54 -0400, Don Clugston <d...@nospam.com> wrote:
This is the way we used to do it, before we had template constraints.
Although it works OK in simple cases, it doesn't scale -- you need to
know all possible template constraints.
I would like to see something in the language conceptually like:
int func(T)(T arg) else { ... }
I'd go further. I'd like to see else if as well.
Currently, you have to repeat conditions from previous template
constraints:
int func(T)(T arg) if (constraint1) {...}
int func(T)(T arg) if (!constraint1 && constraint2)
It's like writing a large if sequence without the benefit of else.
Sometimes you even need to put && !constraint2 in the first version.
for a template which is instantiated only if all constraints have
failed. 'default' is another keyword which could be used, and
'if(false)' is another, but else is probably more natural.
Any attempt to instantiate an 'else' template always results in an
error, just as now. (in practice: if instantiating the else template
didn't trigger a static assert, a generic error message is issued)
Why go this far? Why can't you have an else that's instantiated?
Essentially, you are still forcing this sequence:
int func(T)(T arg) if(constraint) {...}
int func(T)(T arg) if(!constraint) {...}
when the second line could just be:
int func(T)(T arg) else {...}
I don't see the benefit of enforcing the else branch to give an error.
-Steve
