Generic Anonymous Methods by Radek Červinka

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Generic Anonymous Methods
Radek Červinka - 17/May/2020

Спойлер: Content

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In newer Delphi, at least XE3 - I haven't looked deeper, a few generic and anonymous methods are defined in the System.SysUtils unit .

// Generic Anonymous method declarations
type
TProc = reference to procedure;
TProc<T> = reference to procedure (Arg1: T);
TProc<T1,T2> = reference to procedure (Arg1: T1; Arg2: T2);
TProc<T1,T2,T3> = reference to procedure (Arg1: T1; Arg2: T2; Arg3: T3);
TProc<T1,T2,T3,T4> = reference to procedure (Arg1: T1; Arg2: T2; Arg3: T3; Arg4: T4);

TFunc<TResult> = reference to function: TResult;
TFunc<T,TResult> = reference to function (Arg1: T): TResult;
TFunc<T1,T2,TResult> = reference to function (Arg1: T1; Arg2: T2): TResult;
TFunc<T1,T2,T3,TResult> = reference to function (Arg1: T1; Arg2: T2; Arg3: T3): TResult;
TFunc<T1,T2,T3,T4,TResult> = reference to function (Arg1: T1; Arg2: T2; Arg3: T3; Arg4: T4): TResult;

TPredicate<T> = reference to function (Arg1: T): Boolean;

What is this for? One of the uses is a repetitive function that differs in only one part, so we just pass that one part as an anonymous method (in the Browse example, which has a generic function with two parameters as the second parameter).

Спойлер: Code

procedure TForm1.Browse(q: TDataset; pLine: TProc<Integer, TField>);
var
  x     : Integer;
  oField: TField;
begin
  x      := 1;
  oField := q.FieldByName('Name');
  while not q.Eof do
  begin
    pLine(x, oField);
    q.Next;
    inc(x);
  end;

end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Browse(FDQuery1,
    procedure(Line: Integer; Field: TField)
    begin
      memo1.Lines.Add(Format('%d: %s', [Line, Field.AsString]));
    end);

  Browse(FDQuery2,
    procedure(Line: Integer; Field: TField)
    begin
      log.Lines.Add(Format('%d: %s', [Line, Field.AsString]));
    end);
end;

And while I'm at it, further use of anonymous methods is needed in the development for FMX, where a lot of asynchronous dialogs use the same approach, e.g.
TInputCloseDialogProc = reference to procedure(const AResult: TModalResult);

TDialogService = class
…
class procedure ShowMessage(const AMessage: string; const ACloseDialogProc: TInputCloseDialogProc);
…

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