Can operators in Smalltalk be overloaded?

Question

Is it possible to overload operators in Smalltalk?

I am looking for tutorials/examples.

Thanks.

Answer 1

Method overloading is not possible in Smalltalk. Instead, a combination of method overriding and a technique called double dispatch is used to implement the same behavior as operator overloading in other languages.

You can find an example implementation in the mathematical operators +,*,/,- (which are binary messages in Smalltalk). Here is the idea: the implementation of Integer>>+ sends a message #addWithInteger: to its argument. The implementation of #addWithInteger: is implemented on each Magnitude subclass, such as to specialize addition of Int+Int, Float+Int, etc...

Answer 2

For most part, things that are operators in other languages are in Smalltalk unary or binary messages like +, *, /, ... etc. Classes are free to respond to those messages as they seem fit, so yes, you can redefine behavior of +, and you can also make instances of some non number classes understand and respond to it.

For instance look at the implementation of + in Point class.

One thing to note, := and ^ are not messages, so they can not redefined in a way described above.

Btw, for learning Smalltalk, one of the greatest resources of examples and code is the Smalltalk image. So I recommend that you fire up Smalltalk, and learn your way to browse through vast amount of examples that it contains.