Delphi: different PTypeInfo for same type

Question

I am a bit confused about PTypeInfo (and TypeInfo in general) in Delphi - Delphi 10 Seattle to be precise.

I ran into following problem:

We have an ORM framework (based on Spring4D). Now I want to extend it's abilities to map: Nullable integer column to a Nullable field in model. The column contains NULL, 0 or 1. Mapping function is trivial:

• NULL->null (empty Nullable)
• 0->false
• 1-> true

But I believe it does not matter I am working on an ORM. The core of the issue is that for passing the value is used TValue and some casting operations are being made before the final value is assigned to object's field via RTTI. And there I can see the issue I am able to reproduce easily:

The mapping engine provides PTypeInfo pointer for a field. Example:

class declaration
...
MyBooleanField : Nullable<Boolean>;

And somewhere in code:

LMyBooleanField.GetTypeInfo ... result is PTypeInfo to Nullable<System.Boolean>.

And now if I write:

LMyBooleanField.GetTypeInfo = TypeInfo(Nullable<Boolean>)

the result is False. And my ultimate question is WHY? I am sure the types are equal. Both of them return 'Nullable<System.Boolean>' as it's name.

Answer 1

I think that you kind of answer your own question. Although TypeInfo and PTypeInfo are both pointers they are not the same thing. PTypeInfo is a pointer to a location that contains a pointer of type TypeInfo. So LMyBooleanField.GetTypeInfo returns a pointer to a field that points to Nullable< Boolean >, not a pointer to Nullable< Boolean > itself.