Every couple of years, I'll stumble upon yet another Delphi compiler issue.

This time, here's the code that causes the problem.

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program Project4;
{$APPTYPE CONSOLE}
{$R *.res}
 
type
  IFather = interface
    procedure wait; cdecl; overload;
    procedure wait(millis: Int64); cdecl; overload;
    procedure wait(millis: Int64; nanos: Integer); cdecl; overload;
  end;
 
  ISon = interface(IFather)
  end;
 
  TSon = class(TInterfacedObject, ISon)
    procedure wait; cdecl; overload;
    procedure wait(millis: Int64); cdecl; overload;
    procedure wait(millis: Int64; nanos: Integer); cdecl; overload;
  end;
 
{ TSon }
 
procedure TSon.wait;
begin
end;
 
procedure TSon.wait(millis: Int64);
begin
end;
 
procedure TSon.wait(millis: Int64; nanos: Integer);
begin
end;
 
begin
end.

After doing class completion so that method stubs are generated for the wait overloads, the fun begins after trying a compile. The full list of compile errors are as below:

  • [dcc32 Error] Project4.dpr(16): E2169 Field definition not allowed after methods or properties
  • [dcc32 Error] Project4.dpr(17): E2070 Unknown directive: 'wait'
  • [dcc32 Error] Project4.dpr(17): E2029 'END' expected but ')' found
  • [dcc32 Error] Project4.dpr(17): E2029 ',' or ':' expected but ';' found
  • [dcc32 Error] Project4.dpr(18): E2070 Unknown directive: 'wait'
  • [dcc32 Error] Project4.dpr(18): E2029 'END' expected but ')' found
  • [dcc32 Error] Project4.dpr(18): E2029 ',' or ':' expected but ';' found
  • [dcc32 Error] Project4.dpr(19): E2029 Type expected but 'END' found
  • [dcc32 Error] Project4.dpr(15): E2291 Missing implementation of interface method IFather.wait
  • [dcc32 Error] Project4.dpr(15): E2291 Missing implementation of interface method IFather.wait
  • [dcc32 Error] Project4.dpr(27): E2037 Declaration of 'wait' differs from previous declaration
  • [dcc32 Error] Project4.dpr(31): E2037 Declaration of 'wait' differs from previous declaration

I turn to the official documentation and there's no hint to what's wrong. I seem to remember Joe White stumbled upon some issues years ago and he mentioned that there were 2 types of directives, but the solution isn't there.

Eventually, by intuition, I figured out that the overload directive should appear first, and that's it! Rearranging all declarations as follows made the code compile!

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type
  IFather = interface
    procedure wait; overload; cdecl;
    procedure wait(millis: Int64); overload; cdecl;
    procedure wait(millis: Int64; nanos: Integer); overload; cdecl;
  end;
 
  ISon = interface(IFather)
  end;
 
  TSon = class(TInterfacedObject, ISon)
    procedure wait; overload; cdecl;
    procedure wait(millis: Int64); overload; cdecl;
    procedure wait(millis: Int64; nanos: Integer); overload; cdecl;
  end;

In addition, removing the semicolon (;) from the original code works as well.

I filed a bug report and noted the 2 workarounds. Either remove the semicolon, or rearrange method directives so that overload appears first.