CODEWITHSUNDEEP
collectionssmalltalkpharo
user2321611
user2321611

Reputation: 1079

Pharo custom class is not indexable (smalltalk)

I have the following code to create a collection as a member of a class:

 CustomClass new members:Set new; yourself.

next I ask for the size

custom members size.

which results in obviously 0, but when I insert a custom element in the set and I ask for the size it results in an error telling me my custom elements are not indexable.

custom members add: MyCustomElement new.
custom members size.  -> error

Why is this? How does one solve this issue in Smalltalk? Thanks in advance

Upvotes: 1

Views: 581

Answers (1)

aka.nice
aka.nice

Reputation: 9512

The code you exhibit should not trigger the error.
But it's possible that you were bitten by the #add: message.

The #add: message returns the added element, this way you can chain additions like:

collection2 add: (collection1 add: element).

This also work with #at:put: 

collection2 at: j put: (collection1 at: i put: k).

is much like

c2[ j ] = c1[ i ] = k;

Though, if you write something like:

| s e |
e := MyCustomElement new.
s := (Set new) add: e.
^s size

then the variable s will point to the same object than e, an instance of MyCustomElement, and not to the freshly created Set.

Above example thus send the message #size to an instance of MyCustomElement, and this sound very much like the error you described: this may trigger an error because the instances of this class are not indexable.

You can alternatively write:

(s := Set new) add: e.

or use a cascade that ends by sending #yourself to the Set, effectively returning the set itself:

s := (Set new) add: e; yourself.

Upvotes: 1

Related Questions