# Here is the original example: a method from a derived class
# extends the behavior of the baseclass; the primitive "next"
# calls other same-named methods. In the example below, the
# baseclass method "speak" is called at the beginning of the
# derived-class method. The primitive "next" can be placed at
# arbitrary places, or it can be omitted when the baseclass method
# should not be called.
Class BaseClass
BaseClass instproc speak {} {
puts "Hello from BC."
}
Class DerivedClass -superclass BaseClass
DerivedClass instproc speak {} {
next
puts "Hello from DC."
}
DerivedClass create o1
o1 speak
# The output is:
# Hello from BC.
# Hello from DC.
# There are many ways to extend the behavior XOTcl classes
# at runtime. The easiest thing is to add methods dynamically
# to classes. E.g. we can extend the BaseClass with the method
# unknown, which is called whenever an unknown method is called.
BaseClass instproc unknown {m args} {
puts "What? $m? I don't understand."
}
o1 sing
# The output is:
# What? sing? I don't understand.
# Often, you do not want to extend the class, but to
# modifiy the behavior of a single object. In XOTcl, an object
# can have individual methods:
o1 proc sing {} {
puts "Ok, here it goes: Lala Lala!"
}
o1 sing
# The output is:
# Ok, here it goes: Lala Lala!
# In many situations, it is desired to add/remove a set
# of methods dynamically to objects or classes. The mechanisms
# above allow this, but they are rather cumbersome and do
# support a systematic behavior engineering. One can add
# so-called "mixin classes" to objects and/or classes. For
# example, we can define a class M for a more verbose methds:
Class M
M instproc sing {} {
puts -nonewline "[self] sings: "
next
}
M instproc unknown args {
puts -nonewline "[self] is confused: "
next
}
# The behavior of M can be mixed into the beavior of o1 through
# per object mixins ...
o1 mixin M
# ... and we call the methods again:
o1 sing
o1 read
# The output is:
# ::o1 sings: Ok, here it goes: Lala Lala!
# ::o1 is confused: What? read? I don't understand.
# We can remove the new behavior easily by unregistering the
# mixin class ....
o1 mixin ""
# ... and we call the methods again:
o1 sing
o1 read
# The output is:
# Ok, here it goes: Lala Lala!
# What? read? I don't understand.
# Mixin classes can be used to extend the behavior of classes
# as well.
BaseClass instmixin M
o1 sing
o1 read
DerivedClass create o2
o2 read
# The output is:
# ::o1 sings: Ok, here it goes: Lala Lala!
# ::o1 is confused: What? read? I don't understand.
# ::o2 is confused: What? read? I don't understand.Category XOTcl Code