VBA type mismatch error in custom data structure

from VBA help:
Add Method
Adds a member to a Collection object.

Syntax

object.Add item, key, before, after

The Add method syntax has the following object qualifier and named arguments:

Part Description
object Required. An object expression that evaluates to an object in the Applies To list.

item Required. An expression of any type that specifies the member to add to the collection.

key Optional. A unique string expression that specifies a key string that can be used, instead of a positional index, to access a member of the collection.

before Optional. An expression that specifies a relative position in the collection. The member to be added is placed in the collection before the member identified by the before argument. If a numeric expression, before must be a number from 1 to the value of the collection's Count property. If a string expression, before must correspond to the key specified when the member being referred to was added to the collection. You can specify a before position or an after position, but not both.

after Optional. An expression that specifies a relative position in the collection. The member to be added is placed in the collection after the member identified by the after argument. If numeric, after must be a number from 1 to the value of the collection's Count property. If a string, after must correspond to the key specified when the member referred to was added to the collection. You can specify a before position or an after position, but not both.


Remove Method


Removes a member from a Collection object.

Syntax

object.Remove index

The Remove method syntax has the following object qualifier and part:

Part Description
object Required. An object expression that evaluates to an object in the Applies To list.

index Required. An expression that specifies the position of a member of the collection. If a numeric expression, index must be a number from 1 to the value of the collection's Count property. If a string expression, index must correspond to the key argument specified when the member referred to was added to the collection.


Item Method

Returns a specific member of a Collection object either by position or by key.

Syntax

object.Item(index)

The Item method syntax has the following object qualifier and part:

Part Description
object Required. An object expression that evaluates to an object in the Applies To list.

index Required. An expression that specifies the position of a member of the collection. If a numeric expression, index must be a number from 1 to the value of the collection's Count property. If a string expression, index must correspond to the key argument specified when the member referred to was added to the collection.

Oops Misread your question

try:
 Item = main("key")

Nice Graham!

Graham,

That would be the ideal solution except that when the collection is very large, searching by key takes a long time, and it isn't an operation I want to perform twice unless absolutely necessary.

In your example, irregardless of they type of the variant, the Item get property is called twice, which results in a large slowdown.

It seems thenelson provided, more or less, the solution I have been temporarily employing while waiting for something better:

'Retrieves an object with the x, y, z coordinate key specified
Public Function Item(ByVal x As Long, ByVal y As Long, ByVal z As Long) As Variant
    On Error Resume Next
    Set Item = main.Item(str(x)).Item(str(y)).Item(str(z))
    'If this error occured (type mismatch) then the element is a non-object type
    If Err.Number = 13 Then Item = main.Item(str(x)).Item(str(y)).Item(str(z))
    If Err.Number = 5 Then On Error GoTo 0: Err.Raise (5) 'The item does not exist
End Function

If you feel there are no alternatives that allow for a quick and generic retrieval, I'll have to keep it.

--
Alain

"so I hold you responsible for me getting no work done in the last hour ;-)"
OOPS!  LOL ... ok, what ELSE is new!

mx

Assuming Item is declared a variant, does this work?
Set Item = CVar(main.Item(str(x)).Item(str(y)).Item(str(z)))

or this?
Item = CVar(main.Item(str(x)).Item(str(y)).Item(str(z)))

I would at least use Else If to eliminate having to do both tests every time:
    If Err.Number = 13 Then
         Item = main.Item(str(x)).Item(str(y)).Item(str(z))
    ElseIf Err.Number = 5 Then
         On Error GoTo 0: Err.Raise (5) 'The item does not exist
    End If

Graham,
Very clever!  But why are you storing the key in the array? You don't really need it. You don't really use it.

Shouldn't this be called "Colray"? Where does the "...flexion" come from? ;-)

Nelson

Hi Nelson

One of the things that has always annoyed me about collections is that you can't retrieve the key for an item - for example, you can't say:
   strTemp = col(25).Key
This would be very useful for, say, building a TreeView from a collection.

I thought I could solve that problem by storing the key in the item.

"Colflexion" was supposed to imply "flexible collection  ;-)

When I get time (not today!) I'll put some polish on it.  It needs to return a Count property, and also implement a Delete method and enhance the Add to include the other optional arguments.  Of course, the Delete method should do some garbage collection also.

--
Graham

"One of the things that has always annoyed me about collections is that you can't retrieve the key for an item "

Yes ... VERY annoying and weird !

mx

That's what Dictionaries are for... :)

That's a good thought, Graham - wrapping each inserted variant in an node and storing the additional information about the variant type and key in that node. In the data structure I needed, I did something similar, but I hadn't thought of pre-computing the isObject value for later use in retrieval.

"you can't add a UDT to a collection" - not sure if your parenthesized annotation to this comment means what I'm about to say or not, but I did exactly that, just by defining my custom 'Type' as a Class. The downsides to this approach are that it becomes a public class and you have to have a separate class module for it, so I see why you did it the way you did with indexes. Your method also makes it much easier to iterate over all items in the list.


Anyways, I ended up using the 'error handling' method and moving on with my life, but the most agreeable method would certainly have been to store the isObject property on insertion (since I'm working with a custom data structure anyways) and then call upon it at item retrieval time for a quick check of the correct assignment method to use. As such, I'll give you point value for that solution.

--
Alain

Alain,

Did you try the CVar method I suggested in http:#a225744485?

Glad to help and thank you very much for the points with "A" grade!

Happy computing!

Nelson

Hi Nelson

I think the problem is that after using CVar you can't get to any of the properties or methods of the object, which renders it pretty useless :-)

--
Graham

Oh no, the CVar thing actually does nothing. Even if you are casting to Variant with CVar, when it goes to assign the new variable to the next one, it must dynamically type the object (which ignores the casting) to determine whether it will copy by value or by reference (duplicate the variable or create a new reference to the variable). As such, Cvar gives the same errors:

[code]
    Dim avar As Variant
   
   
    Dim str As String
    str = "hello world"
   
    Set avar = CVar(str) 'Err=13 (Type Mismatch Error)
    avar = CVar(str)
   
   
    Dim aobj As Object
    Set aobj = New Collection
   
    Set avar = CVar(aobj)
    avar = CVar(aobj) 'Err = 450 (Wrong number of arguments or invalid property assignment error)
[/code]

--
Alain