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

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

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

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

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

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

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

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