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digitalmars.D - Private Nested Classes?

reply D Man <email example.org> writes:
Is it possible to have private inner nested classes?

For example if I have a class that is only ever used inside 
another class, it would make sense to be able to 'lock' it inside 
the outer class, so that raw instances of it cannot be created.

But in this example: https://run.dlang.io/is/PfemUV

The `private` specifier seems to have no meaning.

Is there a way to get the desired effect (make a nested class 
only accessable from within it's outer class)?
Mar 31 2019
next sibling parent reply Vasyl Teliman <vasniktel gmail.com> writes:
On Sunday, 31 March 2019 at 20:07:39 UTC, D Man wrote:

 Is it possible to have private inner nested classes?

 For example if I have a class that is only ever used inside 
 another class, it would make sense to be able to 'lock' it 
 inside the outer class, so that raw instances of it cannot be 
 created.

 But in this example: https://run.dlang.io/is/PfemUV

 The `private` specifier seems to have no meaning.

 Is there a way to get the desired effect (make a nested class 
 only accessable from within it's outer class)?


Not sure but this looks like a bug.
Mar 31 2019
parent Andre Pany <andre s-e-a-p.de> writes:
On Sunday, 31 March 2019 at 20:23:55 UTC, Vasyl Teliman wrote:

 On Sunday, 31 March 2019 at 20:07:39 UTC, D Man wrote:

 Is it possible to have private inner nested classes?

 For example if I have a class that is only ever used inside 
 another class, it would make sense to be able to 'lock' it 
 inside the outer class, so that raw instances of it cannot be 
 created.

 But in this example: https://run.dlang.io/is/PfemUV

 The `private` specifier seems to have no meaning.

 Is there a way to get the desired effect (make a nested class 
 only accessable from within it's outer class)?


 Not sure but this looks like a bug.


Private works on module level, not on class level. The inner 
class is not accessible from other modules but from the own 
module.

Kind regards
Andre
Mar 31 2019
prev sibling next sibling parent kinke <noone nowhere.com> writes:
On Sunday, 31 March 2019 at 20:07:39 UTC, D Man wrote:

 The `private` specifier seems to have no meaning.


It has; `private` in D applies to the module/file. You'll get a 
deprecation warning if you try to access it in another file; with 
`-de`, it becomes an error.
Mar 31 2019
prev sibling parent =?UTF-8?B?UsOpbXkgTW91w6t6YQ==?= <remy.moueza gmail.com> writes:
On Sunday, 31 March 2019 at 20:07:39 UTC, D Man wrote:

 Is it possible to have private inner nested classes?

 For example if I have a class that is only ever used inside 
 another class, it would make sense to be able to 'lock' it 
 inside the outer class, so that raw instances of it cannot be 
 created.

 But in this example: https://run.dlang.io/is/PfemUV

 The `private` specifier seems to have no meaning.

 Is there a way to get the desired effect (make a nested class 
 only accessable from within it's outer class)?


In D the unit of encapsulation is the module, not the class.

As the main function resides in the same module as the A.Inner 
class, it is visible and no compiler error should occur.

This rules is meant as a simplification of C++ friend classes and 
functions. In D, instead of defining friends, one put related 
class and function into the same module.

To "lock" the class, we need separate the main function from 
class A. This gives a warning (using dmd v2.085.0):
main.d(7): Deprecation: a.A.Inner is not visible from module main

I notice that Inner is defined as "private static", meaning that 
you don't intend to use any reference to the enclosing class 
through `this.outer`.
By putting Inner outside of class A, and having main outside of 
the module, an error occurs:
main.d(7): Error: module `main` class a.Inner is private
main.d(7): Deprecation: a.Inner is not visible from module main
Mar 31 2019