[fpc-pascal] Class helpers and properties

[Sven Barth]

On 27.01.2012 23:51, Mark Morgan Lloyd wrote:
> Sven Barth wrote:
>> On 27.01.2012 22:46, Mark Morgan Lloyd wrote:
>>> If a class has a public reader property like this:
>>>
>>> TLexemeList= class(TObject)
>>> protected
>>> fValue: TPrimaevalValue;
>>> public
>>> property Value: TPrimaevalValue read fValue;
>>> ...
>
> Note that below is in a different unit.
>
>>> is there a way of allowing a class helper to augment this with a
>>> protected writer property? My attempt as below messed up the reader:
>>>
>>> TLLEvaluator = class helper for TLexemeList
>>> private
>>> procedure SetValue(v: TPrimaevalValue);
>>> protected
>>> property Value: TPrimaevalValue write SetValue;
>>> ...
>>>
>>
>> In your exact example fValue is protected so the following should work:
>>
>> property Value: TPrimaevalValue read fValue write SetValue;
>
> That didn't work since once we're in the helper it can't see fValue
> since it's only visible in the original unit.
>

You are right that it does not work, but you're not right about the 
reason. Helpers are able to access published, public and protected 
members of its extended class (e.g. you're able to write "fValue := 
aValue" in your setter inside the helper), but you can't make use of 
fields and methods of the extended class in the helper's declaration.

> Obviously code in the helper can simply call SetValue(), but I thought
> it worth raising in case I was missing something obvious.
>

What about my second suggestion?

Regards,
Sven