Delphi Error – E2568 Can’t create new instance without CONSTRUCTOR constraint in type parameter declaration

Delphi 272 Views 1 Min Read

Delphi Compiler Error

E2568 Can’t create new instance without CONSTRUCTOR constraint in type parameter declaration

Reason for the Error & Solution

This occurs when the generic type is derived from a class that has an implicit constructor and the default constructor clause is not mentioned. 

program E2568;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
TMyClass1 = class

end;
TMyClass2<T: TMyClass1> = class // Fix: replace < T : TmyClass1> with <T : TMyClass1, constructor> 
public
procedure Add;
end;

procedure TMyClass2<T>.Add;
begin
T.Create(nil); //E2568
end;

begin
  Writeln('E2568 Cannot create new instance without CONSTRUCTOR constraint in type parameter declaration');
end.
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