class Test
{
	int foo()
	{
		return 1;
	}
}

void main()
{
	Test test = null;
	int i = test != null ? test.foo() : 0;
}

This throws access violation exception

Max Samuha wrote:
> class Test
> {
> 	int foo()
> 	{
> 		return 1;
> 	}
> }
> 
> void main()
> {
> 	Test test = null;
> 	int i = test != null ? test.foo() : 0;
> }
> 
> This throws access violation exception

From http://www.digitalmars.com/d/expression.html#EqualExpression :

"For class and struct objects, the expression (a == b)  is rewritten as a.opEquals(b), and (a != b) is rewritten as !a.opEquals(b)."

So you have to use "test != null ? test.foo() : 0" for that kind of thing.  Just "test ? test.foo() : 0" works too.

Tydr Schnubbis wrote:
> So you have to use "test != null ? test.foo() : 0" for that kind of thing.  Just "test ? test.foo() : 0" works too.

Oops, I meant "test !is null ? test.foo() : 0".  "is" and "!is" compares the references, it doesn't turn into a call to opEquals.

On Fri, 06 Oct 2006 13:51:21 +0200, Tydr Schnubbis <fake@address.dude> wrote:

>Max Samuha wrote:
>> class Test
>> {
>> 	int foo()
>> 	{
>> 		return 1;
>> 	}
>> }
>> 
>> void main()
>> {
>> 	Test test = null;
>> 	int i = test != null ? test.foo() : 0;
>> }
>> 
>> This throws access violation exception
>
> From http://www.digitalmars.com/d/expression.html#EqualExpression :
>
>"For class and struct objects, the expression (a == b)  is rewritten as a.opEquals(b), and (a != b) is rewritten as !a.opEquals(b)."
>
>So you have to use "test != null ? test.foo() : 0" for that kind of thing.  Just "test ? test.foo() : 0" works too.

Sorry, my fault. I should have used !is or simply test. Thanks

Max Samuha wrote:

>>So you have to use "test != null ? test.foo() : 0" for that kind of thing.  Just "test ? test.foo() : 0" works too.
> 
> Sorry, my fault. I should have used !is or simply test. Thanks

Not entirelly your fault, "== null" and "!= null" is common
enough to have the D compiler detect them at compile time...

Or it could just be defined to "false", like it is in Java.
(i.e. "For any non-null reference x, x == null equals false")

--anders

I like PHP5 syntax for that matter: use == / '!=' to compare values of objects, and === / !== (they call it 'identity operators') to compare references.

This 'identity operators' could be used to distinct, say, true (bool) from 1 (int), etc.. Nice stuff.

-- 
serg.

Serg Kovrov wrote:
> I like PHP5 syntax for that matter: use == / '!=' to compare values of objects, and === / !== (they call it 'identity operators') to compare references.
> 
> This 'identity operators' could be used to distinct, say, true (bool) from 1 (int), etc.. Nice stuff.

=== and !== were in D as well, but supposedly == can't be distinguished from === in some fonts, so they were changed to is and !is..


xs0

Serg Kovrov wrote:

> I like PHP5 syntax for that matter: use == / '!=' to compare values of objects, and === / !== (they call it 'identity operators') to compare references.

We had those in D too... They got renamed to 'is"'and '!is' in 0.126.

--anders

Well, close, but what he's also saying is that PHP (since 4 actually) also dropped implicit conversions for them - for example:

bool foo = true;
int bar = 1;

if (foo is bar)
	writefln("This happens in D but not in PHP.");

This gave you a much faster compare, as well.  Still, I think it makes sense the way it works now in D, personally.

-[Unknown]


> Serg Kovrov wrote:
> 
>> I like PHP5 syntax for that matter: use == / '!=' to compare values of objects, and === / !== (they call it 'identity operators') to compare references.
> 
> We had those in D too... They got renamed to 'is"'and '!is' in 0.126.
> 
> --anders