Howto:Understand Namespaces and Methods: Difference between revisions

== Namespaces ==

A namespace is a "context", i.e. an environment where a certain symbol (variable) is valid.

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.

   house1.bath

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Before namespaces were used, there were only such "global variables", so whenever some piece of code referred to a variable, it was possible to clash with some other similar or even unrelated uses of the variable (imagine a counter variable) somewhere else in the source code.

That's when people started providing a surrounding "context" to embed variables properly.

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

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     print(x);

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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:

  foo.altitude = 100;  

  foo["altitude"] = 100;

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

  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:

Just imagine it like an "area code", where people living in different countries, states, districts, counties, towns get a DIFFERENT prefix code, even though they may have the same telephone number otherwise. The international prefix number (i.e. 001 for the US) makes it obvious that the following number is a US number, same goes for local area codes (752, 642, 543).

== Methods ==

Methods are somewhat related to "namespaces" in that they are class-specific functions (OOP), i.e. functions that are specific to a certain instance of an already instantiated class. In Nasal space, this means that the function is embedded inside a Nasal hash and that it makes use of instance data (using "me") or accessing the parents vector.

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

   house.bath.switch_off_lights

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.

An tutorial along with source code examples going into more detail is available here: [[Howto: Start using vectors and hashes in_Nasal]].

== Resources ==