Please forgive if asked before. My google skills seemed to fail me and didn't see any result from search.

My problem is simple (though not my understanding LOL).

struct D {
      int value;
      bool opEquals()(bool value) const { return (value == value); }
}

D aD;
if (aD == 1) { // OK
}

if (aD) {      //  Error: expression aD of type D does not have a boolean value
}

Is there a way to overload for this? What am I missing?

On Saturday, 21 May 2016 at 18:10:55 UTC, captain_fid wrote:
> Please forgive if asked before. My google skills seemed to fail me and didn't see any result from search.
>
> My problem is simple (though not my understanding LOL).
>
> struct D {
>       int value;
>       bool opEquals()(bool value) const { return (value == value); }
> }
>
> D aD;
> if (aD == 1) { // OK
> }
>
> if (aD) {      //  Error: expression aD of type D does not have a boolean value
> }
>
> Is there a way to overload for this? What am I missing?

struct D {
	int value;

	alias value this;    ///"implicit cast"
	
	bool opEquals()(bool value) const {
	  return (this.value == value); 		///'this.' is required
	}
}

On Saturday, 21 May 2016 at 18:10:55 UTC, captain_fid wrote:
> Please forgive if asked before. My google skills seemed to fail me and didn't see any result from search.
>
> My problem is simple (though not my understanding LOL).
>
> struct D {
>       int value;
>       bool opEquals()(bool value) const { return (value == value); }
> }
>
> D aD;
> if (aD == 1) { // OK
> }
>
> if (aD) {      //  Error: expression aD of type D does not have a boolean value
> }
>
> Is there a way to overload for this? What am I missing?

struct D
{
    int value;

    bool opEquals(T)(T value) const {
        return value == this.value;
    }

    bool opCast(T : bool)() const {
        return this != this.init;  // or some such
    }
}

Not tested, written on my phone so might have missed something.

On Saturday, 21 May 2016 at 18:31:46 UTC, vit wrote:
> On Saturday, 21 May 2016 at 18:10:55 UTC, captain_fid wrote:
>> Please forgive if asked before. My google skills seemed to fail me and didn't see any result from search.
>>
>> My problem is simple (though not my understanding LOL).
>>
>> struct D {
>>       int value;
>>       bool opEquals()(bool value) const { return (value == value); }
>> }
>>
>> D aD;
>> if (aD == 1) { // OK
>> }
>>
>> if (aD) {      //  Error: expression aD of type D does not have a boolean value
>> }
>>
>> Is there a way to overload for this? What am I missing?
>
> struct D {
> 	int value;
>
> 	alias value this;    ///"implicit cast"
> 	
> 	bool opEquals()(bool value) const {
> 	  return (this.value == value); 		///'this.' is required
> 	}
> }

Thanks both vit and anonymouse. (And I couldn't even provide a good example -- didn't mean to use 'value' for opEquals() arg     .... argggggg

Regardless -- vit, your suggestion compiled (and I laughed) but I'm not sure what's getting called. The opEquals() overload doesn't seem to be it. Hard returns of true or false don't seem to impact code. Hmmm.

I'll also check anoymouse's suggestion.

Regardless, thanks for the assistance.

On Saturday, 21 May 2016 at 18:33:53 UTC, Anonymouse wrote:
> On Saturday, 21 May 2016 at 18:10:55 UTC, captain_fid wrote:
>> Please forgive if asked before. My google skills seemed to fail me and didn't see any result from search.
>>
>> My problem is simple (though not my understanding LOL).
>>
>> struct D {
>>       int value;
>>       bool opEquals()(bool value) const { return (value == value); }
>> }
>>
>> D aD;
>> if (aD == 1) { // OK
>> }
>>
>> if (aD) {      //  Error: expression aD of type D does not have a boolean value
>> }
>>
>> Is there a way to overload for this? What am I missing?
>
> struct D
> {
>     int value;
>
>     bool opEquals(T)(T value) const {
>         return value == this.value;
>     }
>
>     bool opCast(T : bool)() const {
>         return this != this.init;  // or some such
>     }
> }
>
> Not tested, written on my phone so might have missed something.

Perfect.. and your 'phoned-in' coding is impressive.

opCast is the biggest thing I was missing/forgetting/misunderstanding here.

I Still need to look back at what is happening with vit's solution.

Sorry again for the bad example to both of you.

On 05/21/2016 12:56 PM, captain_fid wrote:
> On Saturday, 21 May 2016 at 18:33:53 UTC, Anonymouse wrote:
>> On Saturday, 21 May 2016 at 18:10:55 UTC, captain_fid wrote:
>>> Please forgive if asked before. My google skills seemed to fail me
>>> and didn't see any result from search.
>>>
>>> My problem is simple (though not my understanding LOL).
>>>
>>> struct D {
>>>       int value;
>>>       bool opEquals()(bool value) const { return (value == value); }
>>> }
>>>
>>> D aD;
>>> if (aD == 1) { // OK
>>> }
>>>
>>> if (aD) {      //  Error: expression aD of type D does not have a
>>> boolean value
>>> }
>>>
>>> Is there a way to overload for this? What am I missing?
>>
>> struct D
>> {
>>     int value;
>>
>>     bool opEquals(T)(T value) const {
>>         return value == this.value;
>>     }
>>
>>     bool opCast(T : bool)() const {
>>         return this != this.init;  // or some such
>>     }
>> }
>>
>> Not tested, written on my phone so might have missed something.
>
> Perfect.. and your 'phoned-in' coding is impressive.
>
> opCast is the biggest thing I was missing/forgetting/misunderstanding here.

opCast is for explicit type conversions. However, you seem to want implicit type conversions.

> I Still need to look back at what is happening with vit's solution.

vit's 'alias ... this' solution is it. Here is some for info:

  http://ddili.org/ders/d.en/alias_this.html

And here is another example if you want the 'bool' value to be calculated as opposed to being a member:

struct S {
    int x;
    int y;

    /* Implicit type conversion to 'bool'
     * (Because myBoolValue() returns 'bool'.) */
    alias myBoolValue this;

    bool myBoolValue() {
        return (x + y) == 7;    // Some special condition
    }
}

void main() {
    auto a = S(1, 2);
    auto b = S(3, 4);

    assert(!a);    // Calls a.myBoolValue()
    assert( b);    // Calls b.myBoolValue()
}

Ali

On Saturday, 21 May 2016 at 23:06:10 UTC, Ali Çehreli wrote:
> On 05/21/2016 12:56 PM, captain_fid wrote:
> >>> [...]
> fail me
> >>>       [...]
> value); }
> >>> [...]
> have a
> >> [...]
> something.
> > [...]
> missing/forgetting/misunderstanding here.
>
> opCast is for explicit type conversions. However, you seem to want implicit type conversions.
>
> > [...]
> solution.
>
> vit's 'alias ... this' solution is it. Here is some for info:
>
>   http://ddili.org/ders/d.en/alias_this.html
>
> And here is another example if you want the 'bool' value to be calculated as opposed to being a member:
>
> struct S {
>     int x;
>     int y;
>
>     /* Implicit type conversion to 'bool'
>      * (Because myBoolValue() returns 'bool'.) */
>     alias myBoolValue this;
>
>     bool myBoolValue() {
>         return (x + y) == 7;    // Some special condition
>     }
> }
>
> void main() {
>     auto a = S(1, 2);
>     auto b = S(3, 4);
>
>     assert(!a);    // Calls a.myBoolValue()
>     assert( b);    // Calls b.myBoolValue()
> }
>
> Ali

Thanks Ali (and again for making your work so available - I'm almost always re-reading). For some reason, I've missed 'alias this' and it is fascinating.

I'm off to retry these suggestions now...