DIP4: Properties

[Michel Fortin]

On 2009-07-25 08:07:56 -0400, KennyTM~ <kennytm at gmail.com> said:

> Michel Fortin wrote:
>> 
>> In the other thread, I suggested this, which could aleviate the problem:
>> 
>>     int foo.opGet();        // getter
>>     void foo.opAssign(int); // setter
>> 
>> with some support from the compiler.
>> 
>> It could even be exteded to support more:
>> 
>>     int foo.opIndex(int); // foo[1];
>>     void foo.opAddAssign(int); / foo += 1;
>>     void foo.invert(); // special function attached to property
>> 
>> Basically, all you need to implement properties is not a dedicaced 
>> "property" syntax, it's a syntax to implement some kind of local 
>> namespace, and am "opGet" or "opValue" operator for representing the 
>> local namespace. It could also be expressed like this:
>> 
>>     namespace foo {
>>         int opGet(); // getter
>>         void opAssign(int); // setter
>>         ...
>>         int opIndex(int); // foo[1];
>>         void opAddAssign(int); / foo += 1;
>>         void invert(); // special function attached to property
>>     }
>> 
>> In both cases, the result would be the same:
>> 
>>     foo = 1; // same as foo.opAssign(1);
>>     return foo; // same as return foo.opGet();
>> 
> 
> If property is going to be extended like this, why not just make a 
> nested struct. Works even now.

Close, but a nested struct doesn't have access to the outer class, nor 
can you override its functions in a derived class. I'd say what I'm 
proposing is closer to a named mixin:

	class Z
	{
		int x;

		template Property()
		{
			void opAssign(int v) { x = v; }
			void opAddAssign(int v) { x += v; }
			int get() { return x; }

			alias get this;
		}
		mixin Property property;
	}

	Z z = new Z;
	z.property = 1; // works!

What doesn't work here is the "alias get this" line: you're still 
forced to explicitly call the getter. And I have the feeling that 
overriding in a derived class won't work either.

Oh and the syntax isn't great at all.

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/