enumerable class w/o exposing implementation
lazarus / 61-Beginners

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Kays · 2016-03-30 23:49

Hi,

how do I make my class enumerable for a for..in-loop without exposing
anyhow the enumeration implementation by putting the methods
getEnumerator(), moveNext() and property current into the public
section?

The compiler shall be able to enumerate my class just in for..in-
loops, but the user of the class shall not be able to manipulate my
enumerable object, since other objects rely on its state.

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Thaddy · 2016-03-31 07:02

Well, make the getenumeator call (strict) private....
See here for an example that also works in FPC delphi mode:
http://stackoverflow.com/questions/6389357/how-to-properly-make-an-
interface-support-iteration

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Kays · 2016-03-31 16:01

Quote from: Thaddy on March 31, 2016, 09:02:43 amWell, make the
getenumeator call (strict) private....
See here for an example that also works in FPC delphi mode:
http://stackoverflow.com/questions/6389357/how-to-properly-make-an-
interface-support-iteration
Then I get at the for..in-line:
Free Pascal Compiler version 3.0.0 [2015/12/05] for x86_64
Copyright (c) 1993-2015 by Florian Klaempfl and others
Target OS: Linux for x86-64
Compiling myClassTest.pas
myClassTest.pas(42,9) Error: Cannot find an enumerator for the type
"TListEnt"
myClassTest.pas(100) Fatal: There were 1 errors compiling module,
stopping
Fatal: Compilation aborted
Error: /usr/bin/ppcx64 returned an error exitcode

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Thaddy · 2016-04-08 04:57

Try this:
http://blog.marcocantu.com/blog/enumerators_nested_types.html

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Graeme · 2016-04-12 10:55

Take a look at the article (and accompanied source code) I wrote on
the Iterator Design Pattern. [http://geldenhuys.co.uk/articles/]
It is a lot more flexible than the FPC built-in enumerator solution
which can only go forward, can't support regex, can't be reset etc.

The accompanied source code includes enumerators for most used list
classes of FPC. It is very easy to extend. You can even extended it to
iterate say code points of a UTF-8 or UTF-16 encoded string (including
support for surrogate pairs) etc.

Sample usage:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i var  itr:
ITBStringIterator;begin  ...  itr :=
gIteratorFactory.StringIterator(sl);  while itr.HasNext do   
writeln(itr.Next);  ...end; 
Now lets throw some regex in the mix...

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i fitr :=
gIteratorFactory.FilteredStringIterator(MyStringsCollection,
'foob.*r');while fitr.HasNext do  DoSomethingWithItem(fitr.Next); 
Hope you find this useful.