From: Joey Gibson <joey@...>
Date: 2003-11-18T01:10:49+09:00
Subject: Re: Yet Another Rite Thought: method combination

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Gavin Sinclair wrote:

>On Monday, November 17, 2003, 6:22:18 PM, gabriele wrote:
>  
>
>	someone would please explain this to me ?
>  
>
>
>The slide demonstrates it adequately.  Given the above code:
>
>  Foo.new.foo
>  # Output:
>  #   wrap pre
>  #   pre
>  #   foo
>  #   post
>  #   wrap post
>  
>

This is a feature from CLOS that allows you to add hooks to arbitrary 
methods. The names 'pre', 'post' and 'wrap' are predefined and can't be 
changed. This isn't a generic way to sort of chain methods together; 
it's sort of AOP-lite. For any method 'foo' you can define any 
combination of foo:pre, foo:post and foo:wrap. According to Matz, you 
can't change the parameters in a pre, can't change the return value in a 
post, but you CAN do both in a wrap. The output snippet above shows the 
order of calls if you define all three.

Joey


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