Local class definitions
lazarus / 62-General

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simone · 2019-10-04 10:35

As far as I know, local class definitions are not allowed, i.e.
classes must be defined globally, whereas other local type definitions
are possible.

For a project where I'm working (a component based software
engineering tool), this feature could be useful. So I ask if this
possibility will be implemented in the future.

Thanks in advance.

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Thaddy · 2019-10-04 10:41

local class definitions? What is not allowed is this:Code: Pascal
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document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
Test;type   TMyClass = class;beginend;If that is what you mean?
But class definitions local to another class are allowed.
In many cases you can substitute a class with an -advanced - record.
This is allowed:
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 procedure
Test;type   TMyClass = record;beginend;As well as classes that are
local to an implementation section. Which may well be just what you
need if I understand the pattern you describe correctly..

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simone · 2019-10-04 11:38

Thanks Thaddy. You understood perfectly my question. Advanced records
is an option that I had not considered. They could be a good
substitute of classes in my scenario. Your suggestion is very useful
for me.

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marcov · 2019-10-04 11:41

(The reason is probably that a class type generates certain symbols.
Allowing the same name to be allocated as local in various places
would then make symbols clash or need extra mangling in options, makes
this different from other types)

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PascalDragon · 2019-10-05 10:00

Quote from: simone on October 04, 2019, 12:35:33 pmSo I ask if this
possibility will be implemented in the future.Class declarations local
to a routine won't be allowed. Same for advanced records that are not
allowed there either.
If you want something private then you have the whole implementation
section to do as you please.

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simone · 2019-10-05 10:39

Thanks for all the given suggestions. I know that Object Pascal allows
information hiding and specifically encapsulation in many ways. My
question arised from my very specific context and it has been inspired
by the fact that in a program module it is possibile to declare and
define class even if here there are not interface and implementation
sections (required only in unit modules).

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PascalDragon · 2019-10-07 07:32

You can think of the program or library module as consisting only of
an implementation section. If you need to hide something from other
code, then put it in a separate unit (should lead to cleaner code
anyway, as code that is related to each other can then be in one unit
(or multiple related ones)).