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# $Id: s.simpleFilters.xotcl 1.3 01/03/23 22:24:35+01:00 neumann@somewhere.wu-wien.ac.at $
@ @File {
description {
Some simple examples of filters taken from the paper
'Filters as a Language Support for Design Patterns in
Object-Oriented Scripting Languages'. They demonstrate filters,
filter chains and filter inheritance.
}
}
Class A
A metadata add description
A instproc Filter-1 args {
puts " pre-part of [self proc]" ;# pre part
next ;# next call
puts " post-part of [self proc]" ;# post part
}
A instproc printSomething args {
puts " actual called proc: [self proc]"
}
A a1
A filter Filter-1
#a1 set x 1
puts "A call surrounded by pre/post messages:"
a1 printSomething
A filter {}
A instproc Filter-2 args {
puts " only a pre-part in [self proc]"
next
}
A instproc Filter-3 args {
next
puts " only a post-part in [self proc]"
}
A filter {Filter-1 Filter-2 Filter-3}
puts "Now a filter chain:"
a1 printSomething
Class B -superclass A
B instproc Filter-B args {
puts " entering method: [self proc]"
next
}
B b1; B b2
B filter Filter-B
puts "And finally inheritance:"
b1 printSomething
B filter {}
A filter {}
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