[fpc-devel] [] property overloads

[Michael Van Canneyt]

On Mon, 1 Jul 2019, Ondrej Pokorny wrote:

> On 01.07.2019 18:21, Michael Van Canneyt wrote:
>> On Mon, 1 Jul 2019, Ondrej Pokorny wrote:
>>
>>> On 01.07.2019 15:57, Ryan Joseph wrote:
>>>> Yes, I’ve made a patch to allow overriding the actual property 
>>> (https://bugs.freepascal.org/view.php?id=35772).
>>>
>>> Very good! Just a short question: does your solution allow one 
>>> overload without array indexes? It is very useful as a for-in 
>>> enumerator of the array property:
>>>
>>>   TTest = class
>>>   public
>>>     // ...
>>>     property StringArray[Index: Integer]: string read GetString;
>>>     property StringArray: TTestObjectEnumerator read GetString;
>>>   end;
>>
>> I really don't think this should be allowed. You can perfectly do
>>
>> property EnumStringArray: TTestObjectEnumerator read GetString;
>>
>> For S in Mytest.EnumStringArray
>>
>> Typing this extra letters is not going to hurt.
>>
>> Your proposal violates the rule that the resulting type of an 
>> expression must be known when evaluating it.
>>
>> with
>>   Mytest.StringArray
>> it is not clear what the Mytest.StringArray should evaluate to.
>>
>> It can be 2 things:
>>
>> - An array, in which case an index is needed.
>> - An enumerator.
>
> From the above example "Mytest.StringArray" can only evaluate to 
> TTestObjectEnumerator. Nothing else.

Well, this is IMHO not correct. The array is also a possibility.

The compiler encounters Mytest.StringArray - at that point he has 2
possibilities. It's an array (and an index must expected) or it is an
enumerator (and nothing must be expected), but at this point the compiler
cannot decide without looking at the context.

Michael.