Howto:Understand Namespaces and Methods: Difference between revisions

Now, imagine the users of the houses wanting to refer to each bath room using just the word (symbol/variable) "bath". To be able to resolve this properly, they will also need to qualify what house they are referring to, i.e. if it's house1, house2, house3.

Here, houseX is the enclosing namespace/context, i.e. "bath" is a member or "field" of the namespace.

Otherwise, you would have to use different symbols with explicit naming conventions, such as:

As you can see, these naming conventions can become awkward and inflexible pretty quickly:

       var wp1 = 0;

       var wp1alt = 0;

In Nasal space, variables declared in functions will by default be specific to the function's scope and not be directly accessible:

     var hello = func {

       var x =100; # x is local variable specific to the scope of the currently executing function

Here, x is declared to be specific to the "hello" function and its namespace, 'x' will only be valid and visible during the lifetime of function, i.e. at execution time. Consequently, this means that accesses to such variables will be invalid:

     var hello = func {

       var x =100; # x is local variable specific to the scope of the currently executing function

In Nasal, a namespace is just a conventional hash, which is a fancy word for a dictionary. A dictionary stores values in the form of key/value pairs, each value is linked to a key that can be used to look up said value:

  var foo = {};

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To add members or fields to this "context" (or namespace), you can use several different notations, such as using conventional assignment:

  foo.altitude = 100;  

  foo["altitude"] = 100;

or even specify fields during initialization using a key, colon, value notation (key:value):

  var foo = { altitude:100 };

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To add multiple keys to such a dictionary, you just separate them using a comma:

  var foo = { altitude:100, latitude:0, longitude:0 };

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To make this easier you can always add a trailing comma, which is still valid Nasal:

  var foo = { altitude:100, latitude:0, longitude:0, };

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In addition, it is valid to omit the key's value too:

  var foo = { altitude:, latitude:, longitude:, };

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Which will be equivalent to initializing the value to '''nil''':

  var foo = { altitude:nil, latitude:nil, longitude:nil, };

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In order to access these fields or "members" of a namespace, you need to provide a valid namespace first:

So, basically namespaces are all about organizing and structuring your variables and the overall symbol space.

In object oriented programming, this concept is very powerful because you cannot only have hash-specific variables but also hash-specific functions. This makes it possible to create new objects by using a template hash and inheriting fields and behavior (methods).

For example, to switch off the lights in the bath room, there could be a method "switch_off_lights" in the "house" class:

Obviously, this will only work if the switch off routine (method!) has some house to work with. The class itself really is just a "template" for functionality, before it can be used it needs to be instantiated, i.e. a new object (house) must be created using the template, and then the member functions (methods) can be called for that object.