Question

I am using the operator overloading for records in Delphi 2006. (Please don’t answer this question by telling me not to.)

I have two record types with the implicit operator overloaded. They are both only in the implementation of the module, not exposed through the interface.

My problem is, now that they are mutually dependent, I don’t know how to forward declare the second type to the compiler. I know how to do this with functions, procedures, and classes, but not with records.

Here is a simplified example of what I am trying to do:

implementation  type   TMyRec1 = record     Field1 : Integer;     class operator Implicit(a: TMyRec2): TMyRec1;  // <---- Undeclared Identifier here.   end;    TMyRec2 = record     Field2: Integer;     class operator Implicit(a: TMyRec1): TMyRec2;   end;  class operator TMyRec1.Implicit(a:TMyRec2): TMyRec1; begin   Result.Field1 := a.Field2; end;  class operator TMyRec2.Implicit(a:TMyRec2): TMyRec2; begin   Result.Field2 := a.Field1; end; 

Answer 1

You can’t have forward declarations for record types. Define both Implicit operators in the second type:

type   TMyRec1 = record     Field1 : Integer;   end;    TMyRec2 = record     Field2: Integer;     class operator Implicit(a: TMyRec2): TMyRec1;     class operator Implicit(a: TMyRec1): TMyRec2;   end; 

Quoting from the help:

Implicit conversions should be provided only where absolutely necessary, and reflexivity should be avoided. It is best to let type B implicitly convert itself to type A, and let type A have no knowledge of type B (or vice versa).