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digitalmars.D.learn - Static constructors inconsistency

reply "spec" <martins_ajc msn.com> writes:
Hello, i'am experiencing some non consistent behavior with static 
constructors. I wonder if this is some bug or i just don't know 
enough of D (most probably!).. Code example bellow:

//------------------------------------------
module main;

import std.stdio;

class B
{
	static this()
	{
		A a = new A;
		int val = a.getValue("A");
	}
}

class A {
	private static int[string] aa;
	
	static this()
	{
		aa = ["A":1, "B":2];
		writeln("  A static ctor!");
	}

	int getValue(string str)
	{ 	
		return aa[str];	
	}
}



void main(string[] args)
{
	B B = new B;
}
//------------------------------------------

The text "  A static ctor!" never gets printed. The inconsistency 
(IMHO) is that if i do any of this:
- Declare class A before B;
- Change the var declared in A from an AA to some other p.e int;
- Comment the line "int val = a.getValue("A")";

Maybe there are some other points, but at this point i got 
confused and decided trying to understand it. Anyway with any of 
those changes the text gets printed.

Anyone able to shed some light into this?

Cheers,
Apr 26 2014
next sibling parent "spec" <martins_ajc msn.com> writes:
Btw, i only tested this using v2.065.0 of DMD.

Cheers,
Apr 26 2014
prev sibling parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 04/26/2014 12:10 PM, spec wrote:


 Hello, i'am experiencing some non consistent behavior with static
 constructors. I wonder if this is some bug or i just don't know enough
 of D (most probably!).. Code example bellow:

 //------------------------------------------
 module main;

 import std.stdio;

 class B
 {
      static this()
      {
          A a = new A;
          int val = a.getValue("A");
      }
 }

 class A {
      private static int[string] aa;

      static this()
      {
          aa = ["A":1, "B":2];
          writeln("  A static ctor!");
      }

      int getValue(string str)
      {
          return aa[str];
      }
 }



 void main(string[] args)
 {
      B B = new B;
 }
 //------------------------------------------

 The text "  A static ctor!" never gets printed. The inconsistency (IMHO)
 is that if i do any of this:
 - Declare class A before B;
 - Change the var declared in A from an AA to some other p.e int;
 - Comment the line "int val = a.getValue("A")";

 Maybe there are some other points, but at this point i got confused and
 decided trying to understand it. Anyway with any of those changes the
 text gets printed.

 Anyone able to shed some light into this?

 Cheers,


I don't know whether the inconsistency is a bug but according to 
documentation, static this inside a module are executed in lexical 
order: "Static constructors within a module are executed in the lexical 
order in which they appear."

   http://dlang.org/class.html#StaticConstructor

So, if B depends on A then A's static this must appear before B's.

Ali
Apr 26 2014
parent reply "spec" <martins_ajc msn.com> writes:
On Sunday, 27 April 2014 at 02:06:14 UTC, Ali Çehreli wrote:


 I don't know whether the inconsistency is a bug but according 
 to documentation, static this inside a module are executed in 
 lexical order: "Static constructors within a module are 
 executed in the lexical order in which they appear."

   http://dlang.org/class.html#StaticConstructor

 So, if B depends on A then A's static this must appear before 
 B's.

 Ali


Arghh i hate when i make a mistake because i missed something on 
the docs, mainly when i actually read them. Thanks Ali.

Although, yeah, it would be nice if the compiler emitted some 
kind of warning pointing this (if it's at all possible). What got 
me confused was indeed the disparity of results from changing 
small things.

Cheers,
Apr 27 2014
next sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
spec:


 Although, yeah, it would be nice if the compiler emitted some 
 kind of warning pointing this (if it's at all possible). What 
 got me confused was indeed the disparity of results from 
 changing small things.


If you think this can be done and it's useful, then ask for this 
enhancement request in Bugzilla.

Bye,
bearophile
Apr 27 2014
prev sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
spec:


 Although, yeah, it would be nice if the compiler emitted some 
 kind of warning pointing this (if it's at all possible). What 
 got me confused was indeed the disparity of results from 
 changing small things.



D doesn't like warnings, but it could be an error. This is 
minimized code:


struct Foo {
     static this() {
         Bar b;
         int x = b.data[0];
     }
}
struct Bar {
     static int[] data;
     static this() {
         data.length++;
     }
}
void main() {}


A similar example:

struct Foo {
     static this() {
         Bar b;
         int x = b.data[0];
     }
}
struct Bar {
     immutable static int[] data;
     static this() {
         data.length++;
     }
}
void main() {}



Is it possible and a good idea to raise a compilation error in 
such cases where code tries to use Bar static fields before bar 
static this() has run? (But perhaps a more fine-grained error is 
needed, that tracks single fields, to allow more flexible code of 
mutually initializing constructors).

Bye,
bearophile
Apr 27 2014
parent reply "spec" <martins_ajc msn.com> writes:
On Sunday, 27 April 2014 at 13:31:39 UTC, bearophile wrote:

 Is it possible and a good idea to raise a compilation error in 
 such cases where code tries to use Bar static fields before bar 
 static this() has run? (But perhaps a more fine-grained error 
 is needed, that tracks single fields, to allow more flexible 
 code of mutually initializing constructors).

 Bye,
 bearophile


I usually try to refrain myself from opinionating on stuff where 
i lack proper knowledge and i'am still a newbie with D (contrary 
to you bearophile). Having said this, the current behavior did 
confused me and it may very well confuse others in the future. I 
would very much prefer that an error had been thrown, because at 
that point, i would know immediately that it was me who was doing 
something wrong..

Cheers,
Apr 27 2014
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
spec:


 I usually try to refrain myself from opinionating on stuff 
 where i lack proper knowledge and i'am still a newbie with D 
 (contrary to you bearophile).


It's not just a matter of experience, when there are many 
interacting parts it's also a matter of intelligence (and people 
like Timon are more intelligent than me regardless my experience 
in D). If no one comment I'll put this in Bugzilla.

Bye,
bearophile
Apr 27 2014
parent "bearophile" <bearophileHUGS lycos.com> writes:
 If no one comment I'll put this in Bugzilla.


https://issues.dlang.org/show_bug.cgi?id=12667

Bye,
bearophile
Apr 27 2014