How define accepted types in a template parameter?

[Basile B.]

On Saturday, 16 January 2021 at 18:39:03 UTC, Marcone wrote:
> For example, I want my function template to only accept integer 
> or string;

You can do that with either

- `static if` inside the body [1]

   import std.traits;
   void foo(T)(T t)
   {
     static if (isIntegral!T) {}
     else static assert false;
   }


- template constraint [2]

   import std.traits;
   void foo(T)(T t)
   if (isIntegral!T)
   {
   }

- template parameter specialization [3]

   void foo(T : ulong)(T t) // : meaning implictly convert to
   {
   }


2 and 3 being the more commonly used.
1 is more to use the same body instead of using N overloads

[1] : https://dlang.org/spec/version.html#staticif
[2] : https://dlang.org/spec/template.html#template_constraints
[3] : 
https://dlang.org/spec/template.html#parameters_specialization