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4.7: Chapter Summary

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    • A message is always sent to an object named the receiver which may be the result of other message sends.
    • Unary messages are messages that do not require any argument. They are of the form of receiver selector.
    • Binary messages are messages that involve two objects, the receiver and another object and whose selector is composed of one or more characters from the following list: +, --, *, /, |, &, =, >, <, ̃, and @. They are of the form: receiver selector argument
    • Keyword messages are messages that involve more than one object and that contain at least one colon character (:).
    • They are of the form: receiver selectorWordOne: argumentOne wordTwo: argumentTwo
    • Rule One. Unary messages are sent first, then binary messages, and finally keyword messages.
    • Rule Two. Messages in parentheses are sent before any others.
    • Rule Three. When the messages are of the same kind, the order of evaluation is from left to right.
    • In Smalltalk, traditional arithmetic operators such as + and * have the same priority. + and * are just binary messages, therefore * does not have priority over +. You must use parentheses to obtain a different result.

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