Why TFooBaseClass = class of TFooBase in parameter can not compile, but TClass could?

[wqmeng 0]

I have a function which need pass a class referrence in as a parameter.

So I have
 

type

TFooBase = class;

TFooBaseClass = class of TFooBase;

TFooA = class(TFooBase)

end;

TFooB = class(TFooBase)

end;


//Then in another class

type

TBar = class

public

  function FindFooByClass(AFooClass: TFooBaseClass): TFooBase;

end;

implement

function TBar.FindFooByClass(AFooClass: TFooBaseClass): TFooBase;

 

 

Then at the line function TBar.FindFooByClass(AFooClass: TFooBaseClass): TFooBase;

Delphi report
[dcc32 Error] xxx: E2037 Declaration of 'FindFooByClass' differs from previous declaration,  But as you see, the Declaration is same.

 

And if I change TFooBaseClass to be TClass in both the declaration and the implement as

function FindFooByClass(AFooClass: TClass): TFooBase;

function TBar.FindFooByClass(AFooClass: TClass): TFooBase;

Then the source will complile. 

Just want to know that why TFooBaseClass not work?

 

 

Edited Wednesday at 07:17 PM by wqmeng

[Dave Nottage 605]

3 minutes ago, wqmeng said:

So I have

You do not have that. Please provide a complete example, that has the correct spelling of implementation, and the declaration for TFooBase, e.g.

unit Unit2;

interface

type

TFooBase = class;

TFooBaseClass = class of TFooBase;

TFooBase = class

end;


TFooA = class(TFooBase)

end;

TFooB = class(TFooBase)

end;


//Then in another class

type

TBar = class

public

  function FindFooByClass(AFooClass: TFooBaseClass): TFooBase;

end;

implementation

function TBar.FindFooByClass(AFooClass: TFooBaseClass): TFooBase;
begin

end;

end.

Which incidentally, compiles. Also, please just ask your question in one group.

[wqmeng 0]

Hello Dave,

 

Thank you, I just create an empty project and add the code above,  It could compiles.

 

But in my work project, it use the similar approach, get the error as

[dcc32 Error] xxx.pas(517): E2037 Declaration of 'FindIndicatorByClass' differs from previous declaration. 

 

Not sure why.

[wqmeng 0]

Sorry,

 

Find the problem that the 

TFooBaseClass = class of TFooBase;

 

Was defined in two units, after delete one, the problem get fixed.

 

Thanks.

[David Heffernan 2414]

22 hours ago, wqmeng said:

Sorry,

 

Find the problem that the 

TFooBaseClass = class of TFooBase;

 

Was defined in two units, after delete one, the problem get fixed.

 

Thanks.

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