The function of this class is to proxy for the calling parameter to the VM. This class is designed to be used in conjunction with the VMContext class which knows how to get and set values via it, rather than a simple get() or put() from a hashtable-like object. There is probably a lot of undocumented subtlty here, so step lightly. We rely on the observation that an instance of this object has a constant state throughout its lifetime as it's bound to the use-instance of a VM. In other words, it's created by the VelocimacroProxy class, to represent one of the arguments to a VM in a specific template. Since the template is fixed (it's a file...), we don't have to worry that the args to the VM will change. Yes, the VM will be called in other templates, or in other places on the same template, bit those are different use-instances. These arguments can be, in the lingo of the parser, one of :
- Reference() : anything that starts with '$'
- StringLiteral() : something like "$foo" or "hello geir"
- NumberLiteral() : 1, 2 etc
- IntegerRange() : [ 1..2] or [$foo .. $bar]
- ObjectArray() : [ "a", "b", "c"]
- True() : true
- False() : false
- Word() : not likely - this is simply allowed by the parser so we can have syntactical sugar like #foreach($a in $b) where 'in' is the Word
Now, Reference(), StringLit, NumberLit, IntRange, ObjArr are all dynamic things, so their value is gotten with the use of a context. The others are constants. The trick we rely on is that the context rather than this class really represents the state of the argument. We are simply proxying for the thing, returning the proper value when asked, and storing the proper value in the appropriate context when asked. So, the hope here, so an instance of this can be shared across threads, is to keep any dynamic stuff out of it, relying on trick of having the appropriate context handed to us, and when a constant argument, letting VMContext punch that into a local context.
@author
Geir Magnusson Jr.
@version $Id: VMProxyArg.java,v 1.13.4.1 2004/03/03 23:22:56 geirm Exp $