D omit parameter name

original text

import std.conv;

class Foo
{
    
  int i;

  // v===  Derivation type 
  this(int)//(T i)
  {
    
    this.i = i;//.to!int;
  }

  string test()
  {
    
    return i.to!string;
  }
}

void main()
{
    
  long bar = 42;
  auto foo = new Foo(bar);
  assert(foo.test == "42"); // error 
// Cannot pass ` Long ` to ` whole `.
}

---

Parameter names are not required at all , Because this is just an unimplemented declaration , Therefore, the parameter name is not required .
just as Ali said , Parameter not used ( That is to say Template specialization , Virtual function covering , Virtual parameters for overload resolution purposes etc. )

---

TYPE foo(TYPE)() {
     return 42; }
// Function argument list required `()`

TYPE foo(TYPE)() {
    
  int r = 42;
  return r;  // Can't convert ` whole ` to ` short `
}

void main() {
    
  foo!short();
}
struct S(TYPE) {
    
  TYPE foo(TYPE) {
    // This is a function , It's not a template , The type is known , Omit the parameter name 
    return 42;
  }

  //  Function templates 
  TYPE bar(TYPE2)() {
    
    // ...
  }
}