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Howto:Start using vectors and hashes in Nasal: Difference between revisions
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Howto:Start using vectors and hashes in Nasal (view source)
Revision as of 12:18, 8 February 2012
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</syntaxhighlight> | </syntaxhighlight> | ||
Note how this | Note how this creates a vector of 5 waypoints (0..4), each of these waypoints is a full object that can be conveniently accessed: | ||
<syntaxhighlight lang="php"> | <syntaxhighlight lang="php"> | ||
| Line 589: | Line 589: | ||
</syntaxhighlight> | </syntaxhighlight> | ||
As you may remember, the parents keyword points not just to a single "class template" (hash), but instead to a vector of hashes. This makes it possible to use several different hashes as the template for a new hash: | |||
<syntaxhighlight lang="php"> | |||
var new = func return {parents:arg}; | |||
var propulsion = {horse_power:0}; | |||
var vehicle = {tyres:0}; | |||
# create different propulsion classes: | |||
var engine = new(propulsion); | |||
var piston_engine = new (engine); | |||
var turboprop_engine = new(engine); | |||
var jet_engine = new(engine); | |||
var car = new(vehicle, propulsion); | |||
var boat = new(vehicle, propulsion); | |||
var airplane = new(vehicle, propulsion); | |||
# seaplane is a new type of vehicle that inherits from the classes boat and airplane | |||
var seaplane = new(boat, airplane); | |||
</syntaxhighlight> | |||
There are two important concepts to keep in mind here: The relationship between classes is classified according to an "IS A" and "HAS A" pattern: | |||
* a car "IS A" vehicle | |||
* an airplane "IS A" vehicle | |||
* an elephant "IS AN" animal | |||
* a car "HAS AN" engine (0..x) | |||
* an airplane "HAS AN" engine (0..x) | |||
* an elephant "HAS" ears | |||
The difference when dealing with these relationships is that whenever something "IS" something, the right thing to do is to directly create a new object using the parent class: | |||
<syntaxhighlight lang="php"> | |||
var new = func return {parents:arg}; | |||
var animal = {eyes:0,ears:0}; | |||
var dog = new(animal); | |||
var cat = new(animal); | |||
var bird = new(animal); | |||
var spider = new(animal); | |||
</syntaxhighlight> | |||
Now, imagine we wanted to keep the number of legs for each animal, too: 4 legs for dogs and cats, 2 legs for birds and 8 legs for spiders: | |||
<syntaxhighlight lang="php"> | |||
var new = func return {parents:arg}; | |||
var animal = {eyes:0,ears:0,legs:0}; | |||
var dog = new(animal); | |||
var cat = new(animal); | |||
var bird = new(animal); | |||
var spider = new(animal); | |||
</syntaxhighlight> | |||
However, at some point we may need additional information for each leg - such as the length of each leg. That's where we use a new "leg" class (an animal HAS legs), so that the animal class no longer just contains the number of legs, but rather contains a vector of "leg" objects: | |||
<syntaxhighlight lang="php"> | |||
var new = func return {parents:arg}; | |||
var leg = {length:0}; | |||
var animal = {eyes:0,ears:0,legs:[] }; | |||
var dog = new(animal); | |||
var cat = new(animal); | |||
var bird = new(animal); | |||
var spider = new(animal); | |||
</syntaxhighlight> | |||
This was a very simple introduction to object oriented programming in Nasal. | This was a very simple introduction to object oriented programming in Nasal. | ||