[fpc-devel] Delphi anonymous methods

[Vasiliy Kevroletin]

> If the "x" is really located in the FrameObject and that object exists 
> only once then it is rather likely that the output of 'Before 123: ' 
> is different from the output of 'After 123: ', right? Again I think 
> this is a bad thing... 
I was wrong. Local variables of anonymous function located where they 
should be: on stack.

>  So in my opinion an implementation with a stricter division between 
> the single instances of an anonymous function would be the better choice
Am I understand correctly that loop

for i := 1 to 5 do
   procArr[i] := procedure begin
                          DoSmth();
                        end;

should create 5 separate instances?
It is as I thought about closures before. But this is useless without 
capturing of variables by value. During creation of anonymous method you 
*can not bind any values* to it. Anonymous method have only references 
to captured variables. Pascal don't allows to create static variables 
inside function like in c-like languages. So you also not able to create 
unique static variable which available only to one instance of same 
anonymous method. Even if implementation will create many separate 
objects for one anonymous function then all instances will be 
equivalent. Because all instances will refer to same data.

Capturing variables by value will allow simple creation of parametrised 
closures. Now you also can do parametrised anonymous method but you 
should wrap generation of such method into other anonymous function. For 
example like this:

=== example

for i := 1 to 5 do
   procArr[i] := Call(
     function: TProc
     var stored: Integer;
     begin
       stored := i;
       Result := procedure
                 begin
                   Writeln(stored);
                 end;
     end );

===

This can be simplified by support of capturing by value (please don't 
make many attention to syntax, it's not main part of my proposal).

=== example

for i := 1 to 5 do
   procArr[i] := procedure
                        capture i: byValue;
                        begin
                          Writeln(i);
                       end;
     end );

===

What do you think about extension which will allow to specify how to 
capture. Either by value or by reference?

Vasiliy K.