FreePascal RTTI. Is there a way to invoke method?

Question

I'm trying to find out if there is a way to do things similar to Delphi's enhanced RTTI features.

As far as I know FPC doesn't provide RTTI features which appeared in Delphi since Delphi 2010. But I'd like to find some way to do a few tricks during runtime.

Using typinfo unit in FPC I can do such things as:

get Object published property list - via getPropList from typinfo unit;
get/set value of the Object's published property - via GetPropValue(...): Variant/SetPropValue(...Value: Variant);
get published method - via MethodAddres;

But I haven't found a way to do things like:

call methods;
call constructors, or create Objects;

Update: the problem with constructors is much like methods one - I want to have a way to pass different params in it:

// concept of code
type

TClass = class of TObject;

TMyClass1 = class
  public
    constructor Create(Param1: Integer; Param2: string); override;
  end;

TMyClass2 = class
  public
    constructor Create(ObjectParam: Object); override;
  end;

TParams = array of Variant;

var 
Classes: array of TClass 
Instances: array of Object;
ParamArray: array of TParams;

... 

For I := 0 to Count-1 do 
begin
  LocalConstructor := @(Classes[I].Create);
  Instances[I] := CallConstructor(LocalConstructor, ParamArray[I]);
end;

So I need to call constructor without knowing its signature.

So my problem is to call an Object's method and pass some parameters to it. It could look like function CallMethod(Instance: Object; MethodName: String; Params: array of Variant): Variant;

If I'm not mistaken it could be solved via Delphi's 2010+ RTTI. But before using enhanced Delphi's RTTI I'd like to understand is it possible in FPC.

In other words my current problem is pass arguments to a routine. I know it can be done using this scheme:

type
  TmyProc = procedure CallMe(x: byte);
...
  var proc: TmyProc;
...
  proc := pointerToFunc^;
  proc(0);

But I need to implement it without knowing count and types of parameters (during compile time).

There are a few links related to the topic:

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

http://www.swissdelphicenter.ch/torry/showcode.php?id=1745

The second article (http://www.swissdelphicenter.ch/torry/showcode.php?id=1745) describes a way to pass arguments to a routine imported from DLL by name. Which is almost that I need I suppose. But I'm not sure that way is reliable.

Maybe there's any library, which implements these things using "old" typinfo unit (without RTTI unit)?

Also I'm interested in a way to create some kind of universal event handlers - procedures which can be assigned to different events (with different sets of parameters) e.g.:

procedure myEventHandler(params: array of variant);
...
Button.OnClick := myEventHandler;
Button.OnMouseMove := myEventHandler;

is this possible? Or at least something similar to it?

FreePascal RTTI. Is there a way to invoke method?

1 Answers