Question

here is a snippet showing what I am trying to achieve:

type
  TMyObject<T> = class (TObject)
    function GetVarType(Value: T): TVarType;
  end;


function TMyObject<T>.GetVarType(Value: T): TVarType;
var
  TmpValue: Variant;
begin
  TmpValue := Variant(Value); //Invalid typecast
  Result := VarType(TmpValue);
end;

I know that above apporach with typecast is naive but I hope you get the idea. I would like to replace it with some conversion mechanism.

TMyObject will be always of simple type like Integer, String, Single, Double.

The purpose of such conversion is that function VarType gives me integer constant for each simple type which I can store somewhere else.

I would like to know if such conversion is possible?

Thanks for your time.

Answer 1

You can use the RTTI to get this info, just check the value of the TTypeInfo.Kind property:

Check this sample code

{$APPTYPE CONSOLE}

uses
  TypInfo,
  Variants,
  Generics.Collections,
  SysUtils;

type
  TMyObject<T> = class (TObject)
    function GetVarType(Value: T): TVarType;
  end;


function TMyObject<T>.GetVarType(Value: T): TVarType;
begin
  Case PTypeInfo(TypeInfo(T))^.Kind of
    tkInteger : Result:=varInteger;
    tkFloat   : Result:=varDouble;
    tkString  : Result:=varString;
    tkUString : Result:=varUString;
    //add more types here
  End;
end;

Var
  LObj : TMyObject<Integer>;
begin
  try
     Writeln(VarTypeAsText(TMyObject<Integer>.Create.GetVarType(5)));
     Writeln(VarTypeAsText(TMyObject<String>.Create.GetVarType('Test')));
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  Readln;
end.

this will return

Integer
UnicodeString