Re: Call method if declared only

[mipri via Digitalmars-d-learn]

On Friday, 28 February 2020 at 08:08:59 UTC, Виталий Фадеев wrote:
Searching for beauty readable code...

The pattern throughout Phobos is static tests, like isInputRange!R

So something like this:

  import std.stdio;
  import std.traits;

  template canOnKey(T) {
      static if (__traits(hasMember, T, "onKey"))
          enum canOnKey = isCallable!(__traits(getMember, T, 
"onKey"));
      else
          enum canOnKey = false;
  }

  struct A { void onKey() { writeln("called A"); } }
  struct B { }
  struct C { bool onKey = false; }

  void maybeKey(T)(T o) if (canOnKey!T) {
      o.onKey();
  }
  void maybeKey(T)(T o) if (!canOnKey!T) { }

  void main() {
      auto a = A(), b = B(), c = C();
      maybeKey(a);
      maybeKey(b);
      maybeKey(c);
  }

output:

  called A

(and no other output)

Of course in this exact instance it would be simpler to write

  void maybeKey(T)(T o) {
      static if (canOnKey!T)
          o.onKey();
  }

And rather than lots of specific hasThisExactMethod!T tests, it
might be nice if in your actual program there's a 'class' of
grouped properties that you can test for all at once, again
like isInputRange!T and friends.