Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 20:27:09 UTC, Meta wrote: On Friday, 10 March 2017 at 17:08:42 UTC, Whatsthisnow wrote: I guess i am just too used to the java way of x.equals(object) which at the source is exactly 'return this == object' Java would return false here too, though, if it actually did `this == object` in its default compare method. If I remember correctly, comparing two objects with == in Java compares their addresses, not their contents. I must be losing my mind then
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 17:08:42 UTC, Whatsthisnow wrote: I guess i am just too used to the java way of x.equals(object) which at the source is exactly 'return this == object' Java would return false here too, though, if it actually did `this == object` in its default compare method. If I remember correctly, comparing two objects with == in Java compares their addresses, not their contents.
Re: Comparing Instances of Classes
On 03/10/2017 08:22 AM, DRex wrote: Error: function app.A.opEquals does not override any function, did you mean to override 'object.Object.opEquals'? My A class appears exactly as mentioned in your comment... FWIW, here's some other info: http://ddili.org/ders/d.en/object.html#ix_object.opEquals Ali
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:47:47 UTC, Adam D. Ruppe wrote: On Friday, 10 March 2017 at 16:36:17 UTC, DRex wrote: I'm fairly new to D, but this seems to be quite a pain in the rear for a simple comparison of instances of classes...really odd that comparing instances of classes in D requires that messing around when D seems all about simplifying things... There often is no sensible default comparison for class contents (now structs on the other hand do have a default comparison that usually works, but structs don't have to worry about polymorphism), so you just need to specify what fields actually matter to your code... I guess i am just too used to the java way of x.equals(object) which at the source is exactly 'return this == object'
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:36:17 UTC, DRex wrote: I'm fairly new to D, but this seems to be quite a pain in the rear for a simple comparison of instances of classes...really odd that comparing instances of classes in D requires that messing around when D seems all about simplifying things... There often is no sensible default comparison for class contents (now structs on the other hand do have a default comparison that usually works, but structs don't have to worry about polymorphism), so you just need to specify what fields actually matter to your code...
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:30:00 UTC, Adam D. Ruppe wrote:
On Friday, 10 March 2017 at 16:22:18 UTC, DRex wrote:
Error: function app.A.opEquals does not override any function,
did you mean to override 'object.Object.opEquals'?
Oh sorry, maybe I messed up the const. Try:
override bool opEquals(A rhs) { ... }
and if the compiler still complains change the A to Object and
cast it inside (but I'm pretty sure that will work, I think it
is just const it is picky about)
Thanks.
I'm fairly new to D, but this seems to be quite a pain in the
rear for a simple comparison of instances of classes...really odd
that comparing instances of classes in D requires that messing
around when D seems all about simplifying things...
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:22:18 UTC, DRex wrote:
Error: function app.A.opEquals does not override any function,
did you mean to override 'object.Object.opEquals'?
Oh sorry, maybe I messed up the const. Try:
override bool opEquals(A rhs) { ... }
and if the compiler still complains change the A to Object and
cast it inside (but I'm pretty sure that will work, I think it is
just const it is picky about)
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:13:21 UTC, Adam D. Ruppe wrote:
On Friday, 10 March 2017 at 16:08:05 UTC, DRex wrote:
Am I missing something here?
Yeah, you need to implement a custom equality operator.
class A {
int member;
override bool opEquals(const A rhs) {
return this.member == rhs.member; // and other members
that need to be equal
}
}
The default opEquals sees if they are the same *instance* (same
as `a is b`), and does not look at contents. You need to define
that yourself.
I tried the above class A, and now the compiler fails with the
following error:
Error: function app.A.opEquals does not override any function,
did you mean to override 'object.Object.opEquals'?
My A class appears exactly as mentioned in your comment...
Re: Comparing Instances of Classes
On Friday, 10 March 2017 at 16:08:05 UTC, DRex wrote:
Am I missing something here?
Yeah, you need to implement a custom equality operator.
class A {
int member;
override bool opEquals(const A rhs) {
return this.member == rhs.member; // and other members
that need to be equal
}
}
The default opEquals sees if they are the same *instance* (same
as `a is b`), and does not look at contents. You need to define
that yourself.
Comparing Instances of Classes
Hi,
I am trying to compare two instances of a class. I created a
test program to try this, but every method I use to compare the
instances always returns false.
this is my code to test comparison
class A
{
this()
{
}
}
void main()
{
A a = new A();
A a2 = new A();
writeln(equals(a, a2));
}
bool equals(Object obj1, Object obj2)
{
return (obj1 is obj2);
}
I have tried 'a is a2', I have tried 'a1 == a2' and many other
ways (including opEquals from object.d) among other things and
every single time the comparison returns false. The comparison
always fails and never returns true.
I am trying to do something like Object.equals(Object o) in java,
but so far, no success.
Am I missing something here?
