Delphi TProc<Integer> - can parameter value be changed-CodePudding

Can TProc<T> be made to allow aValue not just to be read, but to be edited in a TProc anonymous procedure?

var xProc2: TProc<Integer>;
xProc2 := procedure(aValue: Integer)
  begin
    aValue := 5;
  end;

Delphi 10.4.x

CodePudding user response：

If code requires exactly TProc<Integer>;, then no. You can change local copy of value-type argument and use it inside procedure, but external code doesn't see changes.

If possible, you can use pointer argument of type PInteger, and change aValue^.

Also you can define own generic type with var parameter

type
   TProcvar<T> = reference to procedure (var Arg1: T);

and apply it

var xProc2: TProcVar<Integer>;
xProc2 := procedure(var aValue: Integer)
  begin
    aValue := 5;
  end;

But the most reliable way, I think - use function TFunc<T,TResult> ( or TFunc<TResult> if you don't use input argument)

var xFunc: TFunc<Integer, Integer>;
xfunc := function(aValue: Integer): Integer
  begin
    Result := aValue   5;
  end;