One of the most important facilities in an object-oriented programming language
is ability for a child object to make use of a parent's implementation of some
operation, even when the child provides its own definition for that operation.
pass() function provides this facility in MOO.
this.description; this verb is used by the implementation of the
lookcommand. In many cases, a programmer would like the description of some object to include some non-constant part; for example, a sentence about whether or not the object was `awake' or `sleeping'. This sentence should be added onto the end of the normal description. The programmer would like to have a means of calling the normal
descriptionverb and then appending the sentence onto the end of that description. The function `pass()' is for exactly such situations.
pass calls the verb with the same name as the current verb but as
defined on the parent of the object that defines the current verb. The
arguments given to
pass are the ones given to the called verb and the
returned value of the called verb is returned from the call to
The initial value of
this in the called verb is the same as in the
Thus, in the example above, the child-object's
description verb might
have the following implementation:
return pass() + " It is " + (this.awake ? "awake." | "sleeping.");
That is, it calls its parent's
description verb and then appends to the
result a sentence whose content is computed based on the value of a property on
In almost all cases, you will want to call `pass()' with the same
arguments as were given to the current verb. This is easy to write in MOO;