Why do I have generic anonymous method incompatible type?

anonymous-methods, delphi, delphi-2010, generics

Solution

That is because type inference in Delphi is poor. It could in fact infere `T` from the first parameter but unfortunately the compiler is not satisfied then for the second parameter which would perfectly match.

You have to explicitly state the type parameter like this:

TgrsObj.Using<TStringStream>(TStringStream.Create, procedure(ss: TStringStream)
  begin
    ss.WriteString('test string');
    Memo1.Lines.Text := ss.DataString;
  end);

Problem

In my studying process I use "Coding in Delphi" book by Nick Hodges. I am using Delphi 2010. In the chapter about anonymous methods, he provides a very interesting example about faking .NET `using`. When I try to compile the example, I get an error from the compiler. Please help me to get a result. My class: ``` type TgrsObj = class class procedure Using<T: class>(O: T; Proc: TProc<T>); static; end; implementation { TgrsObj } class procedure TgrsObj.Using<T>(O: T; Proc: TProc<T>); begin try Proc(O); finally O.Free; end; end; ``` Here is how I try to use the code above: ``` procedure TForm4.Button1Click(Sender: TObject); begin TgrsObj.Using(TStringStream.Create, procedure(ss: TStringStream) begin ss.WriteString('test string'); Memo1.Lines.Text := ss.DataString; end); end; ``` Compiler error: ``` [DCC Error] uMain.pas(36): E2010 Incompatible types: 'TProc<ugrsObj.Using<T>.T>' and 'Procedure' ```

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