• =?UTF-8?B?Ikx1w61z?= Marques" <luismarques gmail.com> Mar 12 2013
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> Mar 12 2013
• Timon Gehr <timon.gehr gmx.ch> Mar 13 2013
• "deadalnix" <deadalnix gmail.com> Mar 13 2013

=?UTF-8?B?Ikx1w61z?= Marques" <luismarques gmail.com> writes:

Hi there,

I've been away for a while from the D world, so I guess I missed 
some of the new things.

Regarding opCast, the documentation says:

"This only happens, however, for instances of structs. Class 
references are converted to bool by checking to see if the class 
reference is null or not."

Yet this works:

class B
{
     bool v;

     this(bool v)
     {
         this.v = v;
     }

     T opCast(T)()
     {
         return v;
     }
}

unittest
{
     B bfalse = new B(false);
     B btrue = new B(true);
     assert(cast(bool) bfalse == false);
     assert(cast(bool) btrue == true);
}

Is that a new feature? Can I rely on it? Is it documented 
somewhere?

Thanks! :-)

Regards,
Luís

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/12/2013 01:08 PM, "Luís Marques" <luismarques gmail.com>" wrote:
 Hi there,

 I've been away for a while from the D world, so I guess I missed some of
 the new things.

 Regarding opCast, the documentation says:

 "This only happens, however, for instances of structs. Class references
 are converted to bool by checking to see if the class reference is null
 or not."

 Yet this works:

 class B
 {
 bool v;

 this(bool v)
 {
 this.v = v;
 }

 T opCast(T)()
 {
 return v;
 }
 }

 unittest
 {
 B bfalse = new B(false);
 B btrue = new B(true);
 assert(cast(bool) bfalse == false);
 assert(cast(bool) btrue == true);
 }

 Is that a new feature? Can I rely on it? Is it documented somewhere?

 Thanks! :-)

 Regards,
 Luís


I don't know what the intended behavior but there is a distinction 
between automatic vs. implicit. These pass as well:

     assert(bfalse);
     assert(btrue);

So, apparently implicit conversion considers the class variable and 
explicit conversion considers the class object. And this produces a 
compilation error:

     B bnull;
     assert(cast(bool)bnull);

Error: null dereference in function _D6deneme19__unittestL123991_1FZv

Ali

Timon Gehr <timon.gehr gmx.ch> writes:

On 03/13/2013 12:41 PM, deadalnix wrote:
 On Tuesday, 12 March 2013 at 20:17:33 UTC, Ali Çehreli wrote:
 ...
 So, apparently implicit conversion considers the class variable and
 explicit conversion considers the class object. And this produces a
 compilation error:

     B bnull;
     assert(cast(bool)bnull);

 Error: null dereference in function _D6deneme19__unittestL123991_1FZv

 Ali


 bool toto = bfalse; // Error: cannot implicitly convert expression
 (bfalse) of type module.B to bool

 So it isn't the implicit cast kickin here, but a 3rd behavior. The kind
 of behavior that makes D so special and create theses edges cases we all
 love !


It's an unnecessary special case. assert(objRef); checks whether the 
object reference is not null and then it checks the object invariant. 
Walter thinks this is useful.

"deadalnix" <deadalnix gmail.com> writes:

On Tuesday, 12 March 2013 at 20:17:33 UTC, Ali Çehreli wrote:
 On 03/12/2013 01:08 PM, "Luís Marques" <luismarques gmail.com>" 
 wrote:
 Hi there,

 I've been away for a while from the D world, so I guess I


 the new things.

 Regarding opCast, the documentation says:

 "This only happens, however, for instances of structs. Class


 are converted to bool by checking to see if the class


 or not."

 Yet this works:

 class B
 {
 bool v;

 this(bool v)
 {
 this.v = v;
 }

 T opCast(T)()
 {
 return v;
 }
 }

 unittest
 {
 B bfalse = new B(false);
 B btrue = new B(true);
 assert(cast(bool) bfalse == false);
 assert(cast(bool) btrue == true);
 }

 Is that a new feature? Can I rely on it? Is it documented


 Thanks! :-)

 Regards,
 Luís


 I don't know what the intended behavior but there is a 
 distinction between automatic vs. implicit. These pass as well:

     assert(bfalse);
     assert(btrue);

 So, apparently implicit conversion considers the class variable 
 and explicit conversion considers the class object. And this 
 produces a compilation error:

     B bnull;
     assert(cast(bool)bnull);

 Error: null dereference in function 
 _D6deneme19__unittestL123991_1FZv

 Ali


bool toto = bfalse; // Error: cannot implicitly convert 
expression (bfalse) of type module.B to bool

So it isn't the implicit cast kickin here, but a 3rd behavior. 
The kind of behavior that makes D so special and create theses 
edges cases we all love !