simple (I think) eponymous template question ... what is proper idimatic way ?

[H. S. Teoh]

On Tue, Aug 17, 2021 at 06:11:56PM +0000, james.p.leblanc via Digitalmars-d-learn wrote:
> Evening All,
> 
> Eponymous templates allow a nice calling syntax.  For example, "foo"
> here can be called without needing the exclamation mark (!) at calling
> sites.  We see that foo is restricting a, and b to be of the same type
> ... so far, so good.
> 
> auto foo(T)(T a, T b) { ... }
> 
> Now, suppose I need to restrict "T" only certain subsets of variable
> types.

This is exactly what "signature constraints" are for.  For example:

	auto foo(T)(T a, T b)
	if (is(T == string)) // <--- this is a signature constraint
	{
		... // deal with strings here
	}

	auto foo(T)(T a, T b)
	if (is(T == int)) // you can overload on signature constraints
	{
		... // deal with ints here
	}

	auto foo(T)(T a, T b)
	if (is(T == float) || is(T == double)) // you can use complex conditions
	{
		... // deal with floats or doubles here
	}

Be aware that a signature constraint failure is not an error: the
compiler simply skips that overload of the function.  So if you make a
mistake in a sig constraint, it may *always* fail, and the compiler may
try instead to instantiate a completely unintended overload and generate
an error that may have nothing to do with the actual problem.


T

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