partial class

[KennyTM~]

Denis Koroskin wrote:
> On Fri, 31 Oct 2008 20:06:42 +0300, KennyTM~ <kennytm at gmail.com> wrote:
> 
>> Denis Koroskin wrote:
>>> On Fri, 31 Oct 2008 17:37:42 +0300, Mike James <foo at bar.com> wrote:
>>>
>>>> Not sure if this has been suggested before as an addition to D but 
>>>> what about introducing a partial class as per C# - with all the 
>>>> benefits it would bring...
>>>>
>>>> -=mike=-
>>>   I must be missing something, but D already supports defining class 
>>> methods in one file and implementing them in another one.
>>
>> Something like this:
>>
>>
>> partial class A {
>>      int someMember;
>>      public A(int x) { someMember = x; }
>> }
>>
>> // Far, far apart
>>
>> partial class A {
>>      public int getSomeMember() { return someMember; }
>> }
>>
>>
>> class X {
>>      static void Main() {
>>          var someA = new A(12);
>>          System.Console.WriteLine(someA.getSomeMember());
>>      }
>> }
> 
> Is this worth the trouble? You can have
> 
> class A {
>     int someMember;
>     public A(int x) { someMember = x; }
>     public int getSomeMember();
> }
> 
> in one module and implement getSomeMember() in another module. I believe 
> all the class methods should be defined in one place so that user don't 
> need to import class definition from multiple places. This also makes 
> semantic analysis more complex.

Right. It may be useful when you want to provide additional function, 
e.g. a getRandom method to a NormalDistribution class where normally 
that function would not be needed.

   module math.normaldistrib;

   partial class NormalDistribution : IDistribution {
     double mean() { ... }
     double stdev() { ... }
     // etc.
   }

in another module:

   module random.normal;

   partial class NormalDistribution : IRandomGenerator {
     double getRandom() {
       // complete something the math. package's author
       // don't bother to do.
       ...
     }
   }

But again I said this can be solved with equating a.method(b) to 
method(a,b), which has been in the TODO list long long time ago.

   double getRandom(NormalDistribution nd) {
     // a catch: you can't access private members here.
     ...
   }

.NET uses partial class to separate generated UI code and custom UI 
code, though subclassing the UI look and do the implementation in that 
subclass also solves the problem. (Qt works in this way.)