• pineapple (2/2) Sep 10 2016 I've got a struct and it would be very convenient if I could
• ag0aep6g (14/16) Sep 10 2016 `if (value)` implies a cast to bool. Define opCast!bool and it gets call...
• pineapple (3/21) Sep 10 2016 Huh, I could've sworn that some time ago I tried that and it
• ag0aep6g (2/3) Sep 10 2016 I don't think so.
• Jonathan M Davis via Digitalmars-d-learn (6/33) Sep 10 2016 No. That's how it's been for years now - certainly well before TDPL was
• Steven Schveighoffer (7/10) Sep 12 2016 It's not that way in D1. I think it was added around the time operator

pineapple <meapineapple gmail.com> writes:

I've got a struct and it would be very convenient if I could 
specify what happens when I write `if(value)` - is this possible?

ag0aep6g <anonymous example.com> writes:

On 09/10/2016 04:10 PM, pineapple wrote:
 I've got a struct and it would be very convenient if I could specify
 what happens when I write `if(value)` - is this possible?

`if (value)` implies a cast to bool. Define opCast!bool and it gets called:

----
struct S
{
     bool opCast(T : bool)() { return true; }
}
void main()
{
     S value;
     import std.stdio: writeln;
     if (value) writeln("yup");
}
----

pineapple <meapineapple gmail.com> writes:

On Saturday, 10 September 2016 at 14:24:23 UTC, ag0aep6g wrote:
 On 09/10/2016 04:10 PM, pineapple wrote:
 I've got a struct and it would be very convenient if I could 
 specify
 what happens when I write `if(value)` - is this possible?

 `if (value)` implies a cast to bool. Define opCast!bool and it 
 gets called:

 ----
 struct S
 {
     bool opCast(T : bool)() { return true; }
 }
 void main()
 {
     S value;
     import std.stdio: writeln;
     if (value) writeln("yup");
 }
 ----

Huh, I could've sworn that some time ago I tried that and it 
didn't work. Was this a recent addition to the language?

ag0aep6g <anonymous example.com> writes:

On 09/10/2016 04:29 PM, pineapple wrote:
 Was this a recent addition to the language?

I don't think so.

Jonathan M Davis via Digitalmars-d-learn writes:

On Saturday, September 10, 2016 14:29:33 pineapple via Digitalmars-d-learn 
wrote:
 On Saturday, 10 September 2016 at 14:24:23 UTC, ag0aep6g wrote:
 On 09/10/2016 04:10 PM, pineapple wrote:
 I've got a struct and it would be very convenient if I could
 specify
 what happens when I write `if(value)` - is this possible?

 `if (value)` implies a cast to bool. Define opCast!bool and it
 gets called:

 ----
 struct S
 {

     bool opCast(T : bool)() { return true; }

 }
 void main()
 {

     S value;
     import std.stdio: writeln;
     if (value) writeln("yup");

 }
 ----

 Huh, I could've sworn that some time ago I tried that and it
 didn't work. Was this a recent addition to the language?

No. That's how it's been for years now - certainly well before TDPL was
released - and I suspect that it was that way in D1 (though I've never
really used D1, so I'm not sure).

- Jonathan M Davis

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 9/10/16 6:47 PM, Jonathan M Davis via Digitalmars-d-learn wrote:
 No. That's how it's been for years now - certainly well before TDPL was
 released - and I suspect that it was that way in D1 (though I've never
 really used D1, so I'm not sure).

It's not that way in D1. I think it was added around the time operator 
overloads were changed to templates.

Combined with changelog search and this hint, I think this is correct:

https://github.com/dlang/dlang.org/commit/b60bf3881ccad5e09cfb6e773c3927637ecca70c#diff-87ae512b433ac9f86b715f03fa17cb0e

Version 2.041 added it.

-Steve