On 2017-06-03 18:46, Richmond Mathewson via use-livecode wrote:
Not having looked at any sort of "serious" programming language since
about 1989 (I don't think that VB 6 is a serious language),
I find it hard to understand what a destructor is beyond a way to free
memory on a system that has constraints in that area.
Depends on your definition of 'serious'. I'd say that a language was
'serious' if it allows to write full, complete programs. VB6 certainly
did (after all, it had a huge installed user base for a very long time),
as was HyperCard, as is LiveCode.
1. Does Livecode have something(s) that does the job of a destructor?
Yes.
2. If so, where is it and so on?
The 'delete*' messages are destructors for controls.
On a more general note this thread descended into a discussion of
whether LiveCode is object-oriented or object-based:
https://en.wikipedia.org/wiki/Object-oriented_programming
https://en.wikipedia.org/wiki/Object-based_language
As I've said many times before, object-orientation is a methodology of
programming. Any procedural language which has the equivalent of
(mutable) structs can be used to program in that style relatively
easily. Being 'object-oriented' doesn't mean the language can do any
more than any other, just that it allows you to program in that style
more easily - with compiler checking via explicit syntax for
object-oriented formalisms).
LiveCode certainly has the equivalent of structs (assoc. arrays), and
mutable parameter modes (@ before a parameter). Which means you can do
object-oriented style programming - just as you can in C - indeed I do
this a lot:
command foobarCreate @xSelf
-- init xSelf as an array with the state for foobar
end foobarCreate
command foobarDoSomething @xSelf
-- use state in xSelf array to 'DoSomething'
end foobarDoSomething
As to whether one calls a language object-oriented or not is largely
down to 'what intrinsic features the language gives you to implement the
object-oriented methodology'. In particular, an important feature there
is to be able to define classes, with some form of inheritence and
overriding of methods.
Now, since behaviors were introduced (and then chained behaviors),
LiveCode has had something which is identical to the fundamental ideas
of classes. A behavior script defines a class, the behavior chain allows
inheritence, and the message path along that chain gives you inheritence
and overriding. So, in that sense, LiveCode is definitely
object-oriented.
However, one thing (all?) object oriented languages (in the classical
sense) allow you to do is to define classes, create instances of those
classes and store them in variables - LiveCode doesn't quite have this
(LiveCode variables are either numbers/string or arrays), its
object-orientation is centered around stacks, cards and controls.
(Putting this on a slightly more abstract setting - LiveCode has
object-orientation centered around a persistent object-tree, rather than
transient object instances).
So LiveCode is definitely object-based, but perhaps not quite fully
object-oriented in the classical sense - but it is certainly not that
far off it.
Warmest Regards,
Mark.
--
Mark Waddingham ~ m...@livecode.com ~ http://www.livecode.com/
LiveCode: Everyone can create apps
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