Re: Binary Heap Errors Class level vs function level

[Chris Pons]

Thank you! That helps out quite a bit.

On Thursday, 5 April 2012 at 01:28:12 UTC, Ali Çehreli wrote:

On 04/04/2012 05:24 PM, Chris Pons wrote:
> I'm still messing around with binary heaps. I've successfully
created
> and used it on the function level but for some reason when I
move it to
> the class level I get an error. Furthermore, i'm not entirely
sure how
> to use a binary heap without auto as the type.
>
> class AStar
> {
> ReferenceNode[] openListContainer;
> auto openList = BinaryHeap!(ReferenceNode[], "a.fScore >
> b.fScore")(openListContainer, 0 ); // Error
> }

To get the type, use an alias. Also, only compile-time expressions can be used to initialize members with in-class initializers. So you must initialize openListContainer in a constructor:

import std.container;

struct ReferenceNode
{
    int fScore() @property
    {
        return 0;
    }
}

class AStar
{
    ReferenceNode[] openListContainer;

alias BinaryHeap!(ReferenceNode[], "a.fScore > b.fScore") MyBinaryHeap;

    MyBinaryHeap openList;

    this()
    {
        openList = MyBinaryHeap(openListContainer, 0 );
    }
}

void main()
{
    auto as = new AStar();
}

> Error 1 Error: template instance
BinaryHeap!(ReferenceNode[],"a.fScore >
> b.fScore") BinaryHeap!(ReferenceNode[],"a.fScore > b.fScore")
does not
> match template declaration BinaryHeap(Store,alias less = "a <
b") if
> (isRandomAccessRange!(Store) ||
> isRandomAccessRange!(typeof(Store.init[])))
C:\Users\CP\Documents\Visual
> Studio 2010\Projects\D\STDS\NPC.d 101
>
>
> However this is ok:
>
> class AStar
> {
> void RandomFunction()
> {
> ReferenceNode[] openListContainer;
> openListContainer.length = 500;
> auto openList = BinaryHeap!(ReferenceNode[], "a.fScore >
> b.fScore")(openListContainer, 0 ); //This is ok
> }
> }

That is ok, because now the initial value need not be a compile-time expression. RandomFunction() gets executed and the right-hand side is evaluatod. Fine.

>
> I'd also like to try this, but can't seem to figure it out:
>
> class AStar
> {
> ReferenceNode[] openListContainer;
> auto openList; //no identifier for declarator openlist

That cannot work. Being a statically-typed language, D must know the exact type of the variables at definition time.

> this()
> {
> openListContainer.length = 500;
> openList = = BinaryHeap!(ReferenceNode[], "a.fScore >
> b.fScore")(openListContainer, 0 );
> }
> }
>
> If I know what type openList was, after creating the heap, I
could
> simply use that. I tried using typeid( openList ) to find
out. I got the
> type being something like:
>
> BinaryHeap!(Referencenode[], "a.fScore > b.fScore") openList;
>
> However trying to use this as the type gives me this error:
>
>
> Error 1 Error: template instance
BinaryHeap!(ReferenceNode[],"a.fScore >
> b.fScore") BinaryHeap!(ReferenceNode[],"a.fScore > b.fScore")
does not
> match template declaration BinaryHeap(Store,alias less = "a <
b") if
> (isRandomAccessRange!(Store) ||
> isRandomAccessRange!(typeof(Store.init[])))
C:\Users\CP\Documents\Visual
> Studio 2010\Projects\D\STDS\NPC.d 101
>
>
> Error 2 Error: BinaryHeap!(ReferenceNode[],"a.fScore >
b.fScore") is
> used as a type C:\Users\CP\Documents\Visual Studio
> 2010\Projects\D\STDS\NPC.d 101
>
> I'm just trying to get a variable called openList to the
class level so
> it doesn't keep getting initialized everytime the function is
called.
>
> Any ideas on how to work this out?

I hope the program above is clear. :)

Ali