CODEWITHSUNDEEP
smalltalksqueak
Kumari Sweta
Kumari Sweta

Reputation: 371

Implementation of new with argument in smalltalk

I basically want to implement new which can accept argument e.x obj := SomeClass new: 'a'. I tried to implement this way

initialize: bdata
    data := bdata

But this doesn't work. seems like I am doing some silly mistake because of lack of knowledge. I try to google it but couldn't find any example. Please help.

Upvotes: 3

Views: 364

Answers (3)

Stephen Smith
Stephen Smith

Reputation: 61

You can use the basicNew method if you need to use your argument in the initialize method (as Uko mentions in his answer above). 

withBData: bdata
    ^ (self basicNew bdata: bdata) initialize

Upvotes: 0

codefrau
codefrau

Reputation: 4623

In Smalltalk, new and new: are not keywords, but regular messages. They are simply implemented by the object's class. To write a method for an objects's class (rather than for an instance), click the "class" button in the system browser. There, you could implement your new: method.

Note, however, that it is usually not a good idea to name your own instance creation method new:. Since this is a regular method, you can name it anything you want. For example, MyClass withBData: foo. Make it a nice descriptive name. It could look like

withBData: bdata
    | inst |
    inst := self new.
    inst bdata: bdata.
    ^inst

Upvotes: 4

Uko
Uko

Reputation: 13386

Your code is too short to tell what is wrong. In general you should have an initialize with arg, something like this:

initialize: arg
  self initialize.
  instVar := arg

Then you can implement new: like this:

new: arg
  ^ self basicNew
     initialize: arg;
     yourself

Note that new is implemented as self basicNew initialize, so if you are calling initialize from your custom initialization method, you shouldn't use new in your custom new, use basicNew instead

Upvotes: 4

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