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digitalmars.D - Protected constructors?

reply Michael Coupland <mcoupland hmc.edu> writes:
Is it just me, or should this not compile? (it does)

----------

class Foo
{
	protected this() { }
}

int main( char[][] args )
{
	Foo f = new Foo;
	return 0;
}

----------

The D specs say that "Protected means that only members of the enclosing 
class or any classes derived from that class can access the member." 
However, /something/ outside the class is calling Foo.this()...

I'm writing my own singleton mixin, and I'm trying to keep the rest of 
the world from instantiating any singletons. Is this not the right way 
to approach the problem?

	Michael Coupland
May 21 2004
parent reply Genki Takiuchi <takiuchi khaki.plala.or.jp> writes:
Foo and main are in same module.
So they are friend.

Michael Coupland wrote:

 Is it just me, or should this not compile? (it does)
 
 ----------
 
 class Foo
 {
     protected this() { }
 }
 
 int main( char[][] args )
 {
     Foo f = new Foo;
     return 0;
 }
 
 ----------
 
 The D specs say that "Protected means that only members of the enclosing 
 class or any classes derived from that class can access the member." 
 However, /something/ outside the class is calling Foo.this()...
 
 I'm writing my own singleton mixin, and I'm trying to keep the rest of 
 the world from instantiating any singletons. Is this not the right way 
 to approach the problem?
 
     Michael Coupland

May 21 2004
parent reply Michael Coupland <mcoupland hmc.edu> writes:
Yes, and if I had made the constructor /private/ then I would 
understand; however the constructor is protected... The documentation 
implies that protected (in D) is just a more restricted version of 
private, which prevents /anything/ but derived classes from reaching in. 
Or am I misunderstanding something?

	Michael



Genki Takiuchi wrote:

 Foo and main are in same module.
 So they are friend.
 
 Michael Coupland wrote:
 
 Is it just me, or should this not compile? (it does)

 ----------

 class Foo
 {
     protected this() { }
 }

 int main( char[][] args )
 {
     Foo f = new Foo;
     return 0;
 }

 ----------

 The D specs say that "Protected means that only members of the 
 enclosing class or any classes derived from that class can access the 
 member." However, /something/ outside the class is calling Foo.this()...

 I'm writing my own singleton mixin, and I'm trying to keep the rest of 
 the world from instantiating any singletons. Is this not the right way 
 to approach the problem?

     Michael Coupland


May 21 2004
next sibling parent reply Genki Takiuchi <takiuchi khaki.plala.or.jp> writes:
This may be a bug...

Walter had written in old message:

"Sarat Venugopal" <sarat removeme.huelix.com> wrote in message
news:bogb7f$1cc1$1 digitaldaemon.com...

 1) Are constructors special in that they do not honor protection
 attributes? Apparently, it doesn't matter whether the ctor is private -
 the class can be instantiated regardless.


That's a compiler bug.
 2) Can protection attributes be applied to members of a struct?
 Apparently not.


That should work.
 3) Can a class definition be protected? i.e. I would like a class to be
 visible only within its module.

 private class Foo {...}

 The compiler accepts this but the visbility is public.


That's a bug.
 4) "protected" modifier on a module member is illegal according to the
 docs. But the code compiles all the same and works as if the memeber
 were public. Shouldn't the compiler generate an error here? Of course,
 there is no valid reason to do this, but since there are no warnings
 issued by the compiler, it would be nice to flasg the illegal ones as
 errors.

 Thoughts?

 Cheers,
 Sarat Venugopal

 Some code to illustrate:

 protect.d
 


 import std.c.stdio;

 class CTest
 {
   private:
    this() { printf("Private default ctor\n"); }

    this(int x) { printf("Private int arg ctor\n"); x_ = x; }

   public:
    // Compiler error if this is private
    void Print() { printf("I would like some privacy here\n"); }

 private:
    int x_;
 }

 // Are protection attributes valid in a struct?
 struct STest
 {
   private:
   int x_ = -10;
   int y_ = 100;
 }

 // This is okay
 public STest sPub;

 // This passes - Suppposed to be illegal
 // The line below is quite dumb - just to illustrate
 protected STest sProt;

 // Okay, this is private - compiler error
 // private STest sPriv;

 


 main.d
 


 import protect;

 int main()
 {
    // Test ctor is declared private
    CTest t = new CTest();
    t.Print();

    // x_ and y_ are declared private, but visible
    printf("Public struct (x,y): (%d, %d)\n", sPub.x_, sPub.y_);

    // sProt is a protected module member - should be illegal?
    printf("Protected struct (x,y): (%d, %d)\n", sProt.x_, sProt.y_);

    // Okay, module level privacy is clearly honored
    //printf("Private struct (x,y): (%d, %d)\n", sPriv.x_, sPub.y_);

    return 0;
 }


May 21 2004
parent Michael Coupland <mcoupland hmc.edu> writes:
Ah hah. Thanks very much.
	Michael

Genki Takiuchi wrote:

 This may be a bug...
 
 Walter had written in old message:

May 21 2004
prev sibling parent "Phill" <phill pacific.net.au> writes:
"Michael Coupland" <mcoupland hmc.edu> wrote in message
news:c8mkkl$2bmp$1 digitaldaemon.com...
 Yes, and if I had made the constructor /private/ then I would
 understand; however the constructor is protected... The documentation
 implies that protected (in D) is just a more restricted version of
 private, which prevents /anything/ but derived classes from reaching in.
 Or am I misunderstanding something?

I think you will find that private is more restrictive than protected Phill.
May 22 2004