Listing of doc/example-scripts/per-object-mixins.tcl

Index: doc/example-scripts/per-object-mixins.html =================================================================== diff -u -r23319e802e61ab370472347a8b8506bb650c8cc5 -rc4f449cb353be812ba6502ef8e9587e87881f59b --- doc/example-scripts/per-object-mixins.html (.../per-object-mixins.html) (revision 23319e802e61ab370472347a8b8506bb650c8cc5) +++ doc/example-scripts/per-object-mixins.html (.../per-object-mixins.html) (revision c4f449cb353be812ba6502ef8e9587e87881f59b) @@ -1,966 +1,966 @@ - - - - - -Listing of doc/example-scripts/per-object-mixins.tcl - - - - - -

NX supports "open class definitions", object specific behavior -and mixin classes (among other things) to achieve dynamic behavior -extensions. The so-called per-object mixins are actually an -implementation of the decorator pattern.

package req nx

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.

nx::Class create BaseClass {
-  :public method speak {} {
-    puts "Hello from BC."
-  }
-}
-
-nx::Class create DerivedClass -superclass BaseClass {
-  :public method 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 NX 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 method 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 -modify the behavior of a single object. In NX, an object -can have individual methods:

o1 public method 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 methods:

nx::Class create M {
-  :public method sing {} {
-    puts -nonewline "[self] sings: "
-    next
-  }
-  :method unknown args {
-    puts -nonewline "[self] is confused: "
-    next
-  }
-}

The behavior of M can be mixed into the behavior 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 mixin 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.

- - - + + + + + +Listing of doc/example-scripts/per-object-mixins.tcl + + + + + +

NX supports "open class definitions", object specific behavior +and mixin classes (among other things) to achieve dynamic behavior +extensions. The so-called per-object mixins are actually an +implementation of the decorator pattern.

package req nx

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.

nx::Class create BaseClass {
+  :public method speak {} {
+    puts "Hello from BC."
+  }
+}
+
+nx::Class create DerivedClass -superclass BaseClass {
+  :public method 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 NX 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 method 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 +modify the behavior of a single object. In NX, an object +can have individual methods:

o1 public method 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 methods:

nx::Class create M {
+  :public method sing {} {
+    puts -nonewline "[self] sings: "
+    next
+  }
+  :method unknown args {
+    puts -nonewline "[self] is confused: "
+    next
+  }
+}

The behavior of M can be mixed into the behavior 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 mixin 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.

+ + +