digitalmars.D.learn - User defined types: Problems with ref

Chris (25/25) Jan 23 2014 Here's what I'm trying to do.

Chris (4/30) Jan 23 2014 Sorry in main it is:

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (34/73) Jan 23 2014 createElement does return a reference. However, because D does not have

Chris (14/95) Jan 24 2014 Thank you guys. Yes, it's the array bit that kills the reference

Chris (19/19) Jan 24 2014 Now the output is as it should be (after changing the elements).

FreeSlave (11/37) Jan 23 2014 You can use pointer

Chris (16/63) Jan 23 2014 Thanks, that was fast! Yes I was tinkering around with pointers,

FreeSlave (6/21) Jan 23 2014 Maybe more code will explain more.

FreeSlave (1/1) Jan 23 2014 Anyway, why do you need pointers to elements?

"Chris" <wendlec tcd.ie> writes:

Here's what I'm trying to do.

struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
}

I store Element(s) in an array and want to pass each one by 
reference, which does not work.


class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       return elements[$-1];
     }
}

in main:

auto tag = Element!string("first");

The elements in Tree.elements and the ones in main are not the 
same, instead I obtain a copy of each.
How can I make them refer to the same Elements? If I have to add 
a .ptr property to Element, how do I do that? Is that possible at 
all or did I shoot myself in the foot with the template?

Jan 23 2014

"Chris" <wendlec tcd.ie> writes:

On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Here's what I'm trying to do.

 struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
 }

 I store Element(s) in an array and want to pass each one by 
 reference, which does not work.


 class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       return elements[$-1];
     }
 }

 in main:

 auto tag = Element!string("first");

 The elements in Tree.elements and the ones in main are not the 
 same, instead I obtain a copy of each.
 How can I make them refer to the same Elements? If I have to 
 add a .ptr property to Element, how do I do that? Is that 
 possible at all or did I shoot myself in the foot with the 
 template?

Sorry in main it is:

auto tree = new Tree();
auto tag = tree.createElement("first");

Jan 23 2014

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 01/23/2014 07:26 AM, Chris wrote:

 On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Here's what I'm trying to do.

 struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
 }

 I store Element(s) in an array and want to pass each one by reference,
 which does not work.


 class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       return elements[$-1];
     }
 }

 in main:

 auto tag = Element!string("first");

 The elements in Tree.elements and the ones in main are not the same,
 instead I obtain a copy of each.
 How can I make them refer to the same Elements? If I have to add a
 .ptr property to Element, how do I do that? Is that possible at all or
 did I shoot myself in the foot with the template?

 Sorry in main it is:

 auto tree = new Tree();
 auto tag = tree.createElement("first");

createElement does return a reference. However, because D does not have 
local references the type of tag is Element!string (not 'ref 
Element!string').

The following program demonstrates that the address of the returned 
reference is indeed the same as the one that has been created:

import std.stdio;

struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
}

class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       writefln(" created element at %s", &elements[$-1]);
       return elements[$-1];
     }
}

void main()
{
     auto tree = new Tree();
     writefln("received element at %s", &tree.createElement("first"));
}

Sample output:

  created element at 7F14C72C0F80
received element at 7F14C72C0F80

You can use the returned element directly as well:

     tree.createElement("second").setX("hello");

Ali

Jan 23 2014

"Chris" <wendlec tcd.ie> writes:

On Friday, 24 January 2014 at 01:26:06 UTC, Ali Çehreli wrote:
 On 01/23/2014 07:26 AM, Chris wrote:

 On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Here's what I'm trying to do.

 struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
 }

 I store Element(s) in an array and want to pass each one by


 reference,
 which does not work.


 class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       return elements[$-1];
     }
 }

 in main:

 auto tag = Element!string("first");

 The elements in Tree.elements and the ones in main are not


 the same,
 instead I obtain a copy of each.
 How can I make them refer to the same Elements? If I have to


 add a
 .ptr property to Element, how do I do that? Is that possible


 at all or
 did I shoot myself in the foot with the template?

 Sorry in main it is:

 auto tree = new Tree();
 auto tag = tree.createElement("first");

 createElement does return a reference. However, because D does 
 not have local references the type of tag is Element!string 
 (not 'ref Element!string').

 The following program demonstrates that the address of the 
 returned reference is indeed the same as the one that has been 
 created:

 import std.stdio;

 struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
 }

 class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       writefln(" created element at %s", &elements[$-1]);
       return elements[$-1];
     }
 }

 void main()
 {
     auto tree = new Tree();
     writefln("received element at %s", 
 &tree.createElement("first"));
 }

 Sample output:

  created element at 7F14C72C0F80
 received element at 7F14C72C0F80

 You can use the returned element directly as well:

     tree.createElement("second").setX("hello");

 Ali

Thank you guys. Yes, it's the array bit that kills the reference 
as FreeSlave pointed out. After tinkering around with it, I've 
(reluctantly) turned Element into a class to get the reference 
semantics. I need a reference so I can do things like

tree.getElementById("div");

It's a basic (very simple) HTML / markup thing. Tree stores all 
elements, but the elements are changed outside Tree, like so

auto div = tree.createElement("div");
div.setAttribute("id", "1");
// ...
div.appendChild(...);

etc.

I'm sure there are cleverer ways of implementing a HTML tree.

Jan 24 2014

"Chris" <wendlec tcd.ie> writes:

Now the output is as it should be (after changing the elements).

// The div.toString();
<div class="text" onclick="function();" id="1">
Hello, world!
<span>
I am a span
</span>
</div>

// Tree Elements
[<div class="text" onclick="function();" id="1">
Hello, world!
<span>
I am a span
</span>
</div>
, <span>
I am a span
</span>
]

Jan 24 2014

"FreeSlave" <freeslave93 gmail.com> writes:

On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Here's what I'm trying to do.

 struct Element(T) {
     T x;
     T y;

     public void setX(T value) {
       x = value;
     }
     // More fancy functions ...
 }

 I store Element(s) in an array and want to pass each one by 
 reference, which does not work.


 class Tree {

     Element!string[] elements;

     public ref auto createElement(string name) {
       elements ~= Element!string(name);
       return elements[$-1];
     }
 }

 in main:

 auto tag = Element!string("first");

 The elements in Tree.elements and the ones in main are not the 
 same, instead I obtain a copy of each.
 How can I make them refer to the same Elements? If I have to 
 add a .ptr property to Element, how do I do that? Is that 
 possible at all or did I shoot myself in the foot with the 
 template?

You can use pointer

Tree tree = new Tree();
Element!(string)* element = &tree.createElement("first");

& is to get address of returned value element.

You also can rewrite your function like this:

public Element!(string)* createElement(string name) {
         elements ~= Element!string(name);
         return &elements[$-1];
     }

to return pointer without need to get address on caller side.

Jan 23 2014

"Chris" <wendlec tcd.ie> writes:

On Thursday, 23 January 2014 at 15:34:38 UTC, FreeSlave wrote:
 On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Here's what I'm trying to do.

 struct Element(T) {
    T x;
    T y;

    public void setX(T value) {
      x = value;
    }
    // More fancy functions ...
 }

 I store Element(s) in an array and want to pass each one by 
 reference, which does not work.


 class Tree {

    Element!string[] elements;

    public ref auto createElement(string name) {
      elements ~= Element!string(name);
      return elements[$-1];
    }
 }

 in main:

 auto tag = Element!string("first");

 The elements in Tree.elements and the ones in main are not the 
 same, instead I obtain a copy of each.
 How can I make them refer to the same Elements? If I have to 
 add a .ptr property to Element, how do I do that? Is that 
 possible at all or did I shoot myself in the foot with the 
 template?

 You can use pointer

 Tree tree = new Tree();
 Element!(string)* element = &tree.createElement("first");

 & is to get address of returned value element.

 You also can rewrite your function like this:

 public Element!(string)* createElement(string name) {
         elements ~= Element!string(name);
         return &elements[$-1];
     }

 to return pointer without need to get address on caller side.

Thanks, that was fast! Yes I was tinkering around with pointers, 
but didn't get it right, you did. However, the output is still 
the same, i.e. two different sets:

// After creating and changing
<div id="1">
Hello, world!
<span>
</span>
</div>

// The Elements in Tree.elements:
[<div>
</div>
, <span>
</span>
]

Jan 23 2014

"FreeSlave" <freeslave93 gmail.com> writes:

On Thursday, 23 January 2014 at 15:24:19 UTC, Chris wrote:
 Thanks, that was fast! Yes I was tinkering around with 
 pointers, but didn't get it right, you did. However, the output 
 is still the same, i.e. two different sets:

 // After creating and changing
 <div id="1">
 Hello, world!
 <span>
 </span>
 </div>

 // The Elements in Tree.elements:
 [<div>
 </div>
 , <span>
 </span>
 ]

Maybe more code will explain more.

Note that array requires data to be continuous, so if there are 
no space for new element, it reallocates the whole chunk and 
therefore invalidates old pointers. Use linked list or replace 
struct with class.

Jan 23 2014

"FreeSlave" <freeslave93 gmail.com> writes:

Anyway, why do you need pointers to elements?

Jan 23 2014

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digitalmars.D.learn - User defined types: Problems with ref