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digitalmars.D.learn - new properties for basic types

reply "Dominikus Dittes Scherkl" writes:
Is it possible to write custom properties for basic types, so 
that I can write e.g. "int.myProp" instead of "myProp!int()" 
[analogue to x.myProp instead of myProp(x)]?
Jul 14 2014
parent reply "Puming" <zhaopuming gmail.com> writes:
On Monday, 14 July 2014 at 10:28:30 UTC, Dominikus Dittes Scherkl 
wrote:

 Is it possible to write custom properties for basic types, so 
 that I can write e.g. "int.myProp" instead of "myProp!int()" 
 [analogue to x.myProp instead of myProp(x)]?


yes, just define a funciton with the first parameter int:

```d

 property int triple(int x)
{
   return x * 3;
}

void main()
{
   int x = 4;
   assert(12 == x.triple);
}
```
Jul 14 2014
parent reply Philippe Sigaud via Digitalmars-d-learn writes:
Halas, that's not what the OP wants. He needs properties on the *type*
itself: int.foo instead of foo!int.

So no, this is not possible.
Jul 14 2014
parent reply "Dominikus Dittes Scherkl" writes:
On Monday, 14 July 2014 at 11:28:15 UTC, Philippe Sigaud via 
Digitalmars-d-learn wrote:

 Halas, that's not what the OP wants. He needs properties on the 
 *type*
 itself: int.foo instead of foo!int.


Yes, exactly.


 So no, this is not possible.


Hmm.
So how do I use stuff like this:

     template defaultInit(T)
     {
         static if (!is(typeof({ T v = void; })))    // inout(U)
              property T defaultInit(T v = T.init);
         else
              property T defaultInit();
     }

(this is from std.traits - ok, it's private, but anyway)
Because I have seen nowhere anything like defaultInit!T (or 
T.defaultInit)
and don't understand why here the attribute  property is used.
Why does it make a difference, and how?
Jul 14 2014
parent reply Philippe Sigaud via Digitalmars-d-learn writes:
 Hmm.
 So how do I use stuff like this:

     template defaultInit(T)
     {
         static if (!is(typeof({ T v = void; })))    // inout(U)
              property T defaultInit(T v = T.init);
         else
              property T defaultInit();
     }

 (this is from std.traits - ok, it's private, but anyway)


It should be invoked as `defaultInit!SomeType`



 Because I have seen nowhere anything like defaultInit!T (or T.defaultInit)
 and don't understand why here the attribute  property is used.
 Why does it make a difference, and how?


 property allows you to call a function without the parenthesis (), to
imitate a field in a struct or class.
In this particular case, I don't know what defaultInit is used for. It
seems to compile to a forward declaration of a function, but I don't
know what for.

I cannot find it on my copy of std.traits. What DMD version are you using?
Jul 14 2014
next sibling parent "Dominikus Dittes Scherkl" writes:
On Tuesday, 15 July 2014 at 05:26:57 UTC, Philippe Sigaud via 
Digitalmars-d-learn wrote:

  property allows you to call a function without the parenthesis 
 (), to imitate a field in a struct or class.


Ah, ok. That means without  property I would need to write

defaultInit!T() instead of defaultInit!T

Hmm. I'm not sure that I like this syntax that hides a function 
call.


 In this particular case, I don't know what defaultInit is used 
 for. It seems to compile to a forward declaration of a function,
 but I don't know what for.

 I cannot find it on my copy of std.traits. What DMD version are 
 you using?


Hmm. Ok it was in 2.064. I should update my setup it seems :-)
Jul 15 2014
prev sibling parent "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:
On Tuesday, 15 July 2014 at 05:26:57 UTC, Philippe Sigaud via 
Digitalmars-d-learn wrote:

  property allows you to call a function without the parenthesis 
 (), to
 imitate a field in a struct or class.


That was the original idea, but today the situation is that for 
all argument-less method calls (and UFCS calls) the parentheses 
are optional, but for functions with ` property` parentheses 
_mustn't_ be used. This was mainly done to avoid an ambiguity 
when the function returns something that is itself callable, but 
also is useful to keep APIs stable: If you mark a method as 
` property`, you can replace it by a member variable and existing 
code will not break (but needs to be recompiled, of course).
Jul 15 2014