Another schoolboy question.

Suppose I am constructing a tree (in this case it is an AST).  In C I would have a pointer for the child to find the parent, and an array or linked list of pointers to find the children from the parent.

Obviously, I could still use pointers, but that would not be idiomatic.

I also could just use integer array index references.

A slice seems overkill to refer to just one object, but is that the best way ?

On Wed, Jan 07, 2015 at 02:52:51PM +0000, Laeeth Isharc via Digitalmars-d-learn wrote:
> Another schoolboy question.
> 
> Suppose I am constructing a tree (in this case it is an AST).  In C I would have a pointer for the child to find the parent, and an array or linked list of pointers to find the children from the parent.
> 
> Obviously, I could still use pointers, but that would not be idiomatic.

Not true. If you're using a tree structure, you *should* use pointers. Unless you're using classes, which are by-reference, in which case you can just use the class as-is. :-)


--T

 Not true. If you're using a tree structure, you *should* use
> pointers.
> Unless you're using classes, which are by-reference, in which case you
> can just use the class as-is. :-)

Thanks v much.

I just came to that realization also when I stepped away.

class node
{
	string name;
	node ref;
}

what's wrong with the code above ?  i get an error no identifier for declarator node.  (I have not used classes much, since structs often seem to be enough for what I need to do mostly).

On Wednesday, 7 January 2015 at 15:02:34 UTC, Laeeth Isharc wrote:
>  Not true. If you're using a tree structure, you *should* use
>> pointers.
>> Unless you're using classes, which are by-reference, in which case you
>> can just use the class as-is. :-)
>
> Thanks v much.
>
> I just came to that realization also when I stepped away.
>
> class node
> {
> 	string name;
> 	node ref;
> }
>
> what's wrong with the code above ?  i get an error no identifier for declarator node.  (I have not used classes much, since structs often seem to be enough for what I need to do mostly).

ref is a reserved keyword.

--
Paulo

> ref is a reserved keyword.
doh!

Thanks.

 A slice seems overkill to refer to just one object, but is that
> the best way ?

struct Tree
{
    Tree[] children;
}

Is one way to do it.

On Wednesday, 7 January 2015 at 16:17:47 UTC, Tobias Pankrath wrote:
>  A slice seems overkill to refer to just one object, but is that
>> the best way ?
>
> struct Tree
> {
>     Tree[] children;
> }
>
> Is one way to do it.

You can add some nice sugar for this as well:

struct Tree
{
    this(string data, Tree[] children...)
    {
        this.data = data;
        this.children = children;
    }

    string data;
    Tree[] children;
}

http://dpaste.dzfl.pl/76a8a4c44345

On Wednesday, 7 January 2015 at 20:25:10 UTC, Meta wrote:
> struct Tree
> {
>     this(string data, Tree[] children...)
>     {
>         this.data = data;
>         this.children = children;

Don't do this without `dup`ing. Quoting the documentation:

> An implementation may construct the object or array instance on the stack. Therefore, it is an error to refer to that instance after the variadic function has returned:
[...]
> int[] test(int[] a ...)
> {
>    return a;       // error, array contents invalid after return
>    return a[0..1]; // error, array contents invalid after return
>    return a.dup;   // ok, since copy is made
>}

http://dlang.org/function#variadic

>     }
>
>     string data;
>     Tree[] children;
> }

On Wednesday, 7 January 2015 at 15:04:24 UTC, Paulo  Pinto wrote:
> On Wednesday, 7 January 2015 at 15:02:34 UTC, Laeeth Isharc wrote:
>> Not true. If you're using a tree structure, you *should* use
>>> pointers.
>>> Unless you're using classes, which are by-reference, in which case you
>>> can just use the class as-is. :-)
>>
>> Thanks v much.
>>
>> I just came to that realization also when I stepped away.
>>
>> class node
>> {
>> 	string name;
>> 	node ref;
>> }
>>
>> what's wrong with the code above ?  i get an error no identifier for declarator node.  (I have not used classes much, since structs often seem to be enough for what I need to do mostly).
>
> ref is a reserved keyword.
>
> --
> Paulo

this conversation is so funny: well what's wrong with this . It's a keyword...
Aa Ha ha ha ha , rol.
Seriously, is it so complicated to use a D editor ? I mean with syntax color...

On Wednesday, 7 January 2015 at 23:27:19 UTC, anonymous wrote:
> Don't do this without `dup`ing. Quoting the documentation:

Oh, whoops. I thought those special variadic args were always allocated on the heap.