This example is a straight translation of the OTcl Tutorial -http://www.isi.edu/nsnam/otcl/doc/tutorial.html to NX. It serves as -a very short intro to the basic elements of scripting with NX and -provides a comparison study to OTcl.
package req nx -nx::test configure -count 1
Suppose we need to work with many bagels in our application. We -might start by creating a Bagel class.
% nx::Class create Bagel -::Bagel
We can now create bagels and keep track of them using the info -method.
% Bagel create abagel -::abagel - -% abagel info class -::Bagel - -% Bagel info instances -::abagel
Of course, bagels don’t do much yet. They should remember whether -they’ve been toasted. We can create and access an instance variable -by defining an property for the class. All instance variables are -per default public in the sense of C++.
% Bagel property {toasted 0}Since abagel was created before the definition of the property we -have to set the default value for it using the setter method. Again, -the info method helps us keep track of things.
% abagel info vars - -% abagel configure -toasted 0 - -% abagel info vars -toasted - -% abagel cget -toasted -0
But we really want them to begin in an untoasted state to start -with.
% Bagel create bagel2 -::bagel2 - -% bagel2 info vars -toasted - -% bagel2 cget -toasted -0
Our bagels now remember whether they’ve been toasted. Let is -recreate the first one.
% lsort [Bagel info instances] -::abagel ::bagel2 - -% ::abagel destroy - -% Bagel info instances -::bagel2 - -% Bagel create abagel -::abagel
Now we’re ready to add a method to bagels so that we can toast -them. Methods have an argument list and body like regular -Tcl procs. Here’s the toast method.
% Bagel public method toast {} { - if {[incr :toasted] > 1} then { - error "something's burning!" - } -} -::nsf::classes::Bagel::toast
The defined methods can be queried with info. We see as well the -setter method for the variable toasted.
% Bagel info methods -toast
Aside from setting the toasted variable, the body of the toast -method demonstrates how to access instance variables by using a -leading colon in the name.
We invoke the toast method on bagels in the same way we use the -info and destroy methods that were provided by the system. That -is, there is no distinction between user and system methods.
% abagel toast -% abagel toast -something's burning!
Now we can add spreads to the bagels and start tasting them. If we -have bagels that aren’t topped, as well as bagels that are, we may -want to make toppable bagels a separate class. Let explore -inheritance with these two classes, starting by making a new class -SpreadableBagel that inherits from Bagel. A SpreadableBagel has an -property toppings which might have multiple values. Initially, -toppings are empty.
% nx::Class create SpreadableBagel -superclass Bagel { - :property -incremental {toppings:0..n ""} -} -::SpreadableBagel - -% SpreadableBagel cget -superclass -::Bagel -% SpreadableBagel info superclasses -::Bagel - -% SpreadableBagel info heritage -::Bagel ::nx::Object
Let’s add a taste method to bagels, splitting its functionality -between the two classes and combining it with next.
% Bagel public method taste {} { - if {${:toasted} == 0} then { - return raw! - } elseif {${:toasted} == 1} then { - return toasty - } else { - return burnt! - } -} -::nsf::classes::Bagel::taste - -% SpreadableBagel public method taste {} { - set t [next] - foreach i ${:toppings} { - lappend t $i - } - return $t -} -::nsf::classes::SpreadableBagel::taste - -% SpreadableBagel create abagel -::abagel - -% abagel toast -% abagel toppings add jam -jam -% abagel toppings add m&m -m&m jam - -% abagel taste -toasty m&m jam
Of course, along come sesame, onion, poppy, and a host of other -bagels, requiring us to expand our scheme. We could keep track of -flavor with an instance variable, but this may not be -appropriate. Flavor is an innate property of the bagels, and one -that can affect other behavior - you wouldn’t put jam on an onion -bagel, would you? Instead of making a class hierarchy, let’s use -multiple inheritance to make the flavor classes mixins that add a -their taste independent trait to bagels or whatever other food they -are mixed with.
% nx::Class create Sesame { - :public method taste {} {concat [next] "sesame"} -} -::Sesame - -% nx::Class create Onion { - :public method taste {} {concat [next] "onion"} -} -::Onion - -% nx::Class create Poppy { - :public method taste {} {concat [next] "poppy"} -} -::Poppy
Well, they don’t appear to do much, but the use of next allows them -to be freely mixed.
% nx::Class create SesameOnionBagel -superclass SpreadableBagel -mixin {Sesame Onion} -::SesameOnionBagel - -% SesameOnionBagel create abagel -toppings butter -::abagel - -% abagel taste -raw! butter onion sesame
For multiple inheritance, the system determines a linear inheritance -ordering that respects all of the local superclass orderings. You -can examine this ordering with an info option. next follows this -ordering when it combines behavior.
% SesameOnionBagel info heritage -::Sesame ::Onion ::SpreadableBagel ::Bagel ::nx::Object - -% abagel info precedence -::Sesame ::Onion ::SesameOnionBagel ::SpreadableBagel ::Bagel ::nx::Object
We can also combine our mixins with other classes, classes that need -have nothing to do with bagels, leading to a family of chips.
% nx::Class create Chips { - :public method taste {} {return "crunchy"} -} -::Chips - -% nx::Class create OnionChips -superclass Chips -mixin Onion -::OnionChips - -% OnionChips create abag -::abag - -% abag taste -crunchy onion