Expanders

Infusion component options, as written in fluid.defaults blocks, go through a process called expansion when they are used to instantiate a component. Two kinds of expansion happen during this process -

• Expansion of IoC references, written as strings in the form "{context}.path" as a result of the Value Resolution process, and
• Expansion of expanders, which are blocks of JSON occurring in the options with the key expander

The standard use of an expander is to designate a function to be called when instantiating the component options, which produces a value based on processing the expander arguments. This can be useful when static definition of a default option is not possible.

Expanders are specified using the keyword "expander" in the component defaults:

fluid.defaults("component.name", {
    optionName: {
        expander: {
            ...
        }
    }
});

The basic form of an expander record is very similar to that of an Invoker - it contains entries func/funcName together with args to designate the function call which will produce the required options values.

Examples

This example locates the global function named "cspace.search.modelFilter" and calls it with the arguments given by resolving the context "{searchView}" - in this case, most likely the top-level component defined in defaults itself. The return value from this function is then placed in the options of the instantiated component (the "fluid.pager") at the path modelFilter:

fluid.defaults("cspace.search.searchView", {
    components: {
        resultsPager: {
            type: "fluid.pager",
            options: {
                modelFilter: {
                    expander: {
                        func: "cspace.search.makeModelFilter",
                        args: ["{searchView}"]
                    }
                }
            }
        }
   }
});

The fluid.noexpand expander

The fluid.noexpand expander is a very specialised expander that normal users of the framework should not require to use. It has been retained in the framework for completeness, but its effects should normally be obtained using a mergePolicy of "noexpand". This expander simply dumps its literal argument (held at a path named value or tree) into the component's options without expansion.

Example:

fluid.defaults("cspace.specBuilder", {
    components: {
        specBuilderImpl: {
            type: "cspace.specBuilderImpl",
            options: {
                unexpanded: {
                    expander: {
                        type: "fluid.noexpand",
                        value: "{specBuilder}.urlExpander"
                    }
                }
            }
        }
    }
});