Why doesn't C++ support strongly typed ellipsis?

c++ variadic-functions ellipsis
Nicholas Hamilton picture Nicholas Hamilton · Aug 28, 2015 · Viewed 7.8k times · Source

Can someone please explain to me why C++, at least to my knowledge, doesn't implement a strongly typed ellipsis function, something to the effect of:

void foo(double ...) {
 // Do Something
}

Meaning that, in plain speak: 'The user can pass a variable number of terms to the foo function, however, all of the terms must be doubles'

Answer

edmz picture edmz · Aug 28, 2015

There is 

 void foo(std::initializer_list<double> values);
 // foo( {1.5, 3.14, 2.7} );

which is very close to that.

You could also use variadic templates but it gets more discursive. As for the actual reason I would say the effort to bring in that new syntax isn't probably worth it: how do you access the single elements? How do you know when to stop? What makes it better than, say, std::initializer_list?

C++ does have something even closer to that: non-type parameter packs.

template < non-type ... values>

like in

template <int ... Ints>
void foo()
{
     for (int i : {Ints...} )
         // do something with i
}

but the type of the non-type template parameter (uhm) has some restrictions: it cannot be double, for example.

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