Delphi: Call a function whose name is stored in a string

Question

Is it possible to call a function whose name is stored in a string in Delphi?

Answer 1

If you are asking if there is something like the JavaScript eval() is possible in Delphi, no this is not (easily) achievable since Delphi compiles to native code.

If you need only to support some strings you can always do many if or a case... Something like:

if myString = 'myFunction' then
    myFunction();

Answer 2

I'm surprised no one has suggested a dispatch table. This is exactly what it's for.

program RPS;

uses
  SysUtils,
  Generics.Collections;

type
  TDispatchTable = class(TDictionary<string, TProc>);

procedure Rock;
begin
end;

procedure Paper;
begin
end;

procedure Scissors;
begin
end;

var
  DispatchTable: TDispatchTable;

begin
  DispatchTable := TDispatchTable.Create;
  try
    DispatchTable.Add('Rock', Rock);
    DispatchTable.Add('Paper', Paper);
    DispatchTable.Add('Scissors', Scissors);

    DispatchTable['Rock'].Invoke; // or DispatchTable['Rock']();
  finally
    DispatchTable.Free;
  end;
end.

The implementation I wrote uses generics so it would only work with Delphi 2009+. For older versions it would probably be easiest to implement using TStringList and the command pattern

Answer 3

function ExecuteMethod(AClass : TClass; AMethodName : String; const AArgs: Array of TValue) : TValue;
var
  RttiContext : TRttiContext;
  RttiMethod  : TRttiMethod;
  RttiType    : TRttiType;
  RttiObject  : TObject;
begin
  RttiObject := AClass.Create;
  try
    RttiContext := TRttiContext.Create;
    RttiType    := RttiContext.GetType(AClass);
    RttiMethod  := RttiType.GetMethod(AMethodName);
    Result      := RttiMethod.Invoke(RttiObject,AArgs);
  finally
    RttiObject.Free;
  end;
end;

Answer 4

You can do something like this by crafting one or more classes with published properties that use functions to implement their read and write functionality. The properties can then be discovered using RTTI reflection and referenced, causing the underlying functions to get called.

Alternatively, you can store function pointers in a table, or even the Object property of TStringList and effectively index them by string name.

Straight calling of a function by name is not possible in Delphi.