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Added section on temporary classes

closure/master
Mike Gerwitz 2011-03-15 00:31:09 -04:00
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commit 7c4efe5f2a
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@ -133,6 +133,7 @@ capital, for class names (and nothing else).
@menu
* Anonymous vs. Named Classes::
* Temporary Classes:: Throwaway classes that only need to be used once
@end menu
@ -200,3 +201,46 @@ functionally no difference between named and anonymous classes.}
Much better! We now have a useful error message and immediately know which class
is causing the issue.
@node Temporary Classes
@subsection Temporary Classes
In @ref{f:class-easejs,}, we saw that the @code{new} keyword was unnecessary
when instantiating classes. This permits a form of shorthand that is very useful
for creating @dfn{temporary classes}, or ``throwaway`` classes which are used
only once.
Consider the following example:
@float Figure, f:class-tmp
@verbatim
// new instance of anonymous class
var foo = Class(
{
'public bar': function()
{
return 'baz';
}
} )();
foo.bar(); // returns 'baz'
@end verbatim
@caption{Declaring a temporary (throwaway) class}
@end float
In @ref{f:class-tmp,} above, rather than declaring a class, storing that in a
variable, then instantiating it separately, we are doing it in a single command.
Notice the parenthesis at the end of the statement. This invokes the
constructor. Since the @code{new} keyword is unnecessary, a new instance of the
class is stored in the variable @var{foo}.
We call this a temporary class because it is used only to create a single
instance. The class is then never referenced again. Therefore, we needn't even
store it - it's throwaway.
The downside of this feature is that it is difficult to notice unless the reader
is paying very close attention. There is no keyword to tip them off. Therefore,
it is very important to clearly document that you are storing an instance in the
variable rather than an actual class definition. If you follow the CamelCase
convention for class names, then simply do not capitalize the first letter of
the destination variable for the instance.