• Era Scarecrow (23/23) Apr 29 2012 In some code I'm working on, my asserted when I've confirmed it
• Jonathan M Davis (5/33) Apr 29 2012 == uses opEquals, not opCmp. It's using Object's opEquals, which does a
• Era Scarecrow (3/8) Apr 29 2012 Ahhh of course. Personally I think opCmp includes opEquals... At
• Jonathan M Davis (7/16) Apr 29 2012 I believe that there are two major reasons why opEquals is separate:

"Era Scarecrow" <rtcvb32 yahoo.com> writes:

  In some code I'm working on, my asserted when I've confirmed it 
was correct. With the opCmp() overridden.  'this' refers to the 
current object, so why doesn't the first one succeed?

class X {
   int z;

   this(int xx) {
	z = xx;
   }

   override int opCmp(Object y){
	X x = cast(X) y;
	return z - x.z;
   }

   void something(X rhs) {
     assert(this.opCmp(rhs) == 0); //works fine.
     assert(this == rhs); 	  //fails?
   }
}

int main(){
	X a = new X(10);
	X b = new X(10); //different objects, same compare value
	a.something(b);
	return 0;
}

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Monday, April 30, 2012 07:09:46 Era Scarecrow wrote:
   In some code I'm working on, my asserted when I've confirmed it
 was correct. With the opCmp() overridden.  'this' refers to the
 current object, so why doesn't the first one succeed?
 
 class X {
    int z;
 
    this(int xx) {
 	z = xx;
    }
 
    override int opCmp(Object y){
 	X x = cast(X) y;
 	return z - x.z;
    }
 
    void something(X rhs) {
      assert(this.opCmp(rhs) == 0); //works fine.
      assert(this == rhs); 	  //fails?
    }
 }
 
 int main(){
 	X a = new X(10);
 	X b = new X(10); //different objects, same compare value
 	a.something(b);
 	return 0;
 }

== uses opEquals, not opCmp. It's using Object's opEquals, which does a 
comparison of the references, so it's true when comparing the exact same 
object and false otherwise.

- Jonathan M Davis

"Era Scarecrow" <rtcvb32 yahoo.com> writes:

On Monday, 30 April 2012 at 05:22:56 UTC, Jonathan M Davis wrote:
 == uses opEquals, not opCmp. It's using Object's opEquals, 
 which does a
 comparison of the references, so it's true when comparing the 
 exact same
 object and false otherwise.

  Ahhh of course. Personally I think opCmp includes opEquals... At 
least I only have to deal with 2 compare functions and not more.

Jonathan M Davis <jmdavisProg gmx.com> writes:

On Monday, April 30, 2012 07:28:16 Era Scarecrow wrote:
 On Monday, 30 April 2012 at 05:22:56 UTC, Jonathan M Davis wrote:
 == uses opEquals, not opCmp. It's using Object's opEquals,
 which does a
 comparison of the references, so it's true when comparing the
 exact same
 object and false otherwise.

 
   Ahhh of course. Personally I think opCmp includes opEquals... At
 least I only have to deal with 2 compare functions and not more.

I believe that there are two major reasons why opEquals is separate:

1. Many types of objects can have equality but less than and greater than 
comparisons would make no sense for them.

2. It's more efficient to check for equality with opEquals than it would be
with 
opCmp.

- Jonathan M Davis