Example Method in Beck's Smalltalk Best Practice Patterns

[bprior]

Kent Beck uses this example on page 3 of his Introduction:

Part>>* aRate

     ^Part

           amount: amount * aRate

           date:date

Station>>computePart: aPart

     ^aPart * self rate

It looks like the method selector in the first line is * aRate.  I haven't seen this syntax before. Am I missing something? Or is it a typo? Or?

[Johnmci]

2*3

Someone has to implement the *

Say Integer>>* aNumber

 ^aNumber productFromInteger: self

PS double dispatch here 

Sent from my iPhone

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[Bert Freudenberg]

It's not syntax but convention: Class>>selector means the selector implemented by Class. The actual method in the system browser would look like

* aRate

^...

- Bert -

[Bruce Prior]

Bert, I understand Class>>selector. But why has he included the asterisk? Isn't a selector name supposed to be one word? I'm assuming the asterisk is intended as the binary multiply method. Shouldn't it be be included only in the actual method?

Bruce

[Bert Freudenberg]

Rate>>* is just an example of Class>>selector. 

There are three kinds of selectors in Smalltalk: unary (single word, e.g. "5 negated"), binary (non-letters, e.g. "3 * 4"), and keyword (one or more words ending in a colon, e.g. "4 between: 3 and: 5"). So 'negated', '*', and 'between:and:' are valid selectors. 

- Bert -

[Bruce Prior]

Bert, thanks for this. Until now I didn't appreciate this view of the binary message characters as selectors. I've got it now. ("AhHa!")

Bruce

[Bert Freudenberg]

You're welcome. Btw, this sort of question would be very much appreciated on our beginners list - many others could learn from them:

http://lists.squeak.org/mailman/listinfo/beginners

- Bert -