Weird UFC and opCall issues

[Ali Çehreli via Digitalmars-d-learn]

On 01/03/2015 12:26 PM, Darrell wrote:

 > Fails with:
 >      t.d(34): Error: need 'this' for 'opCall' of type 'int()'
 >
 > Also opCall seems to be required to create a range.

D has a feature that does not exists e.g. in C++: You can call the type 
itself as a function. The 'Test()' syntax is a call to that type's 
static opCall().

 >
 > class Test
 > {
 >    int opCall()
 >    {
 >      return 1;
 >    }

Not being static, that would require an instance of the Test class.

 >
 >    @property int front()
 >    {
 >      return 2;
 >    }

You may want to define that member function 'const' as well.

 >
 >    void popFront()
 >    {
 >    }
 >
 >    @property bool empty()
 >    {
 >      return false;
 >    }

That can be 'const' as well.

 >
 > };

D does not require that semicolon.

 >
 > void main(){
 >    ubyte [] p1;
 >    Test();
 > }

I am removing the opCall and assuming that you actually want a ubyte I 
am returning a ubyte from front().

Also note the almost-mandatory-with-ranges convenience function 'test()' 
below, which hides the invocation of 'new':

class Test
{
   @property ubyte front()
   {
     return 2;
   }

   void popFront()
   {
   }

   @property bool empty()
   {
     return false;
   }
}

Test test()
{
     return new Test();
}

/* Alternatively, you can move test() inside Test as a static opCall:

     static Test opCall()
     {
         return new Test();
     }

Then, the syntax in main could be

     ubyte [] p1 = Test().take(3).array;

*/

import std.stdio;
import std.range;

void main(){
   ubyte [] p1 = test().take(3).array;
   assert(p1 == [ 2, 2, 2 ]);
}

Ali