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37
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1 # Everything is a message in Io, apparently. Everything.
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2 # Messages have senders, receivers and args, and you can get and use those objects.
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3 # So the example makes a post office.
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4 postOffice := Object clone
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5 # Add a method that returns the sender object
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6 postOffice packageSender := method(call sender)
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7 "Post office: " print
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8 postOffice println
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9 mailer := Object clone
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10 # Call the PostOffice's method
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11 mailer deliver := method(postOffice packageSender)
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12 "Mailer: " print
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13 mailer println
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14 # Calling the method returns the caller (sender via the postOffice object)
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15 mailer deliver println
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16
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17 # We can also get message arguments and name
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18 # Let's do this a little differently to the book!
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19 postOffice messageDetails := method(call message name println; call message arguments println)
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20 postOffice messageDetails("One", 2, :three)
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21
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22 # Because of how args are passed unevaluated then we can make our own "unless" method
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23 unless := method(
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24 (call sender doMessage(call message argAt(0))) \
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25 ifFalse(call sender doMessage(call message argAt(1))) \
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26 ifTrue(call sender doMessage(call message argAt(2)))
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27 )
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28 # Note the line continuations - this seems more readable than the approach in the book of
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29 # leaving the "ifFalse(" and "ifTrue(" on the previous line!
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30 # Also, this is an IF in the form "[boolean statement] ifFalse(code) ifTrue(code)", not the earlier
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31 # "if(boolean, true-code, false-code)" form
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32
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33 unless (1 == 2, write("One is not two\n"), write("OMG! Maths has broken!!!!\n")) |
