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digitalmars.D.learn - dcollections ArrayList pb with mixin template

reply BLS <windevguy hotmail.de> writes:
Hi, I have a problem with a mixin template. More exact with an 
Arraylist!T within a mixin template.
Given.
void main() {
	auto p = new Person("Hans", 32);
	p ~= new Person("Steve", 40);
	p ~= new Person("Bjoern", 101);
}	

class Person {
	private	string _name;
	private uint _age;
	
	mixin TLinkList;
	
	this(string name, uint age) {
		this._name = name;
		this._age = age;
	}
}
	
mixin template TLinkList() {
	alias typeof(this) T;
	alias ArrayList!T TList;
	
	T[] pa;
	auto pl = new TList(pa);  // This does not work !
	void opCatAssign(T v) {
		pa ~= v;
	}	
}
Error: non-constant expression new ArrayList(pa)	main.d	

Ideas ?
Thanks Bjoern
Jul 01 2010
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 01 Jul 2010 15:36:53 -0400, BLS <windevguy hotmail.de> wrote:


 Hi, I have a problem with a mixin template. More exact with an  
 Arraylist!T within a mixin template.
 Given.
 void main() {
 	auto p = new Person("Hans", 32);
 	p ~= new Person("Steve", 40);
 	p ~= new Person("Bjoern", 101);
 }	

 class Person {
 	private	string _name;
 	private uint _age;
 	
 	mixin TLinkList;
 	
 	this(string name, uint age) {
 		this._name = name;
 		this._age = age;
 	}
 }
 	
 mixin template TLinkList() {
 	alias typeof(this) T;
 	alias ArrayList!T TList;
 	
 	T[] pa;
 	auto pl = new TList(pa);  // This does not work !
 	void opCatAssign(T v) {
 		pa ~= v;
 	}	
 }
 Error: non-constant expression new ArrayList(pa)	main.d	

 Ideas ?
 Thanks Bjoern


I'm thinking it has to do with you trying to create a member with that  
line.

I think a member initializer has to be a constant expression, like int i =  
1.  Anything else has to be done in the constructor.  This kinda sucks,  
because you can't initialize members with their defaults where you declare  
them, but it's the way D works.

-Steve
Jul 01 2010
next sibling parent BLS <windevguy hotmail.de> writes:
On 01/07/2010 22:59, Steven Schveighoffer wrote:

 On Thu, 01 Jul 2010 15:36:53 -0400, BLS <windevguy hotmail.de> wrote:


 Hi, I have a problem with a mixin template. More exact with an
 Arraylist!T within a mixin template.
 Given.
 void main() {
 auto p = new Person("Hans", 32);
 p ~= new Person("Steve", 40);
 p ~= new Person("Bjoern", 101);
 }

 class Person {
 private string _name;
 private uint _age;

 mixin TLinkList;

 this(string name, uint age) {
 this._name = name;
 this._age = age;
 }
 }

 mixin template TLinkList() {
 alias typeof(this) T;
 alias ArrayList!T TList;

 T[] pa;
 auto pl = new TList(pa); // This does not work !
 void opCatAssign(T v) {
 pa ~= v;
 }
 }
 Error: non-constant expression new ArrayList(pa) main.d

 Ideas ?
 Thanks Bjoern


 I'm thinking it has to do with you trying to create a member with that
 line.

 I think a member initializer has to be a constant expression, like int i
 = 1. Anything else has to be done in the constructor. This kinda sucks,
 because you can't initialize members with their defaults where you
 declare them, but it's the way D works.

 -Steve


Thanks for the feedback Steve.
IMHO it should work.. One reason is that C.E. Miller has created a 
Circularly-linked list module, containing a portable linked list 
template mixin. Indeed Christophers implementation is  different in that 
the LinkList is part of the mixin template...

http://www.dprogramming.com/list.php

2) Commenting the auto pl = new TList() line out makes the snippet work.

mixin template TLinkList() {
	alias typeof(this) T;
	alias ArrayList!T TList;
	
	T[] pa;
	//auto pl = new TList(pa);  // NOW IT WORKS !
	void opCatAssign(T v) {
		pa ~= v;
	}	
Well I am a D noob.  Have to investigate a bit more, and of course any 
help is welcome :)

Bjoern
Jul 01 2010
prev sibling parent reply bearophile <bearophileHUGS lycos.com> writes:
Steven Schveighoffer:

 I think a member initializer has to be a constant expression, like int i =  
 1.  Anything else has to be done in the constructor.


There are the static constructors too, for modules, structs, classes.

Bye,
bearophile
Jul 01 2010
next sibling parent reply BLS <windevguy hotmail.de> writes:
On 02/07/2010 00:26, bearophile wrote:

 Steven Schveighoffer:

 I think a member initializer has to be a constant expression, like int i =
 1.  Anything else has to be done in the constructor.


 There are the static constructors too, for modules, structs, classes.

 Bye,
 bearophile


Hi bearophile,
I don't understand (in this context) . Can you please elaborate a bit more ?

thanks bjoern
Jul 01 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
BLS:

 I don't understand (in this context) . Can you please elaborate a bit more ?


I have not shown you code because I don't understand your context. But you can
put inside static this() {...} code that can't be run statically, like the
initialization of a run-time thing.

Bye,
bearophile
Jul 01 2010
parent BLS <windevguy hotmail.de> writes:
On 02/07/2010 00:47, bearophile wrote:

 BLS:

 I don't understand (in this context) . Can you please elaborate a bit more ?


 I have not shown you code because I don't understand your context. But you can
put inside static this() {...} code that can't be run statically, like the
initialization of a run-time thing.

 Bye,
 bearophile


Indeed, the sample snippet was bad 'cause I don't use static.

mixin template TLinkList() {
     alias typeof(this) T;
     //alias LinkList!T TList;

     STATIC T[] pa;
     //static TList list; //= new TList(pa);  // This does not work !

     void opCatAssign(T v) {
         pa ~= v;
     }
...
}

// every struct respective class like
class x {
   // enhanced with
    mixin TlinkList
}
can be used like every other linked list.  (stack, queue, whatever)
well, at least this is my intention.
bjoern
Jul 02 2010
prev sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 01 Jul 2010 18:26:06 -0400, bearophile <bearophileHUGS lycos.com>  
wrote:


 Steven Schveighoffer:

 I think a member initializer has to be a constant expression, like int  
 i =
 1.  Anything else has to be done in the constructor.


 There are the static constructors too, for modules, structs, classes.


static constructors don't help initialize member variables.

-Steve
Jul 02 2010