partial class

[Denis Koroskin]

On Fri, 31 Oct 2008 20:59:23 +0300, KennyTM~ <kennytm at gmail.com> wrote:

> 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.)

Note that partial classes also compromise code security:

partial class Foo
{
     private int secret;
}

// HA-HA-HACK!
partial class Foo
{
     int hack() { return secret; }
}

I wouldn't trust these.