[fpc-pascal] Unrelated type helpers with the same members? Implement an interface with a type helper?

[Andrew Haines]

So, I came up with a solution using Custom Attributes.

I can declare this:

[TEnumAttr('YES', 'NO', 'COULD_BE')]
   TMyEnum = (meYes, meNo, meCouldBe);

and at runtime look for the TEnumAttr attribute and use that.


TEnumAttr = class(TCustomAttribute)
   protected
     FValues: TStringArray;
     FTypeName: String;
   public
     class function FromType(ATypeInfo: PTypeInfo): TEnumAttr;
     constructor Create(Val1: String);
     constructor Create(Val1, Val2: String);

etc

Maybe this can help someone else with a similar use case.


Regards,

Andrew Haines

On 12/22/22 8:40 PM, Andrew Haines via fpc-pascal wrote:
> Hi what I want to do is similar to this question here: 
> https://en.delphipraxis.net/topic/423-rtti-determine-record-helper-type-for-a-base-type/
>
> I am going to create multiple type helpers for enums and I would like 
> to look up the helper and use common methods AsString AsOrdinal to 
> get/set the values. I am recieving them as json that I dont have 
> control over. I am using typeinfo to fill in all the properties but I 
> would like to convert the strings I am receiving to the enum values 
> semi-automatically.
>
> LString := 'STATUS';
>
> LHelper := GetHelper(LPropInfo^.PropType); // enum proptype
>
> LToStringInterface := LHelper as IToStringInterface;
>
> SetOrdProp(LObject, 'propname', LToStringInterface.OrdValue(LString);
>
>
> Something like that. I'm not sure if it's even possible to find the 
> helper type with typeinfo.
>
> Thanks for your suggestions :)
>
> Regards,
>
> Andrew
>
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