Latest builds of the Sciter have decorators implemented. My implementation of decorators ideologically derived from the same decorator feature in Python of Guido van Rossum.
Decorators is a meta/macro-programming feature that allows to transform or update function or class defined in source code.
Here is an example: say we are designing some dialog with various input elements and buttons. Usually code behind such dialogs is a collection of simple “if-we’ve-got-some-event-here-then-update-state-over-there” blocks. First part (if-we’ve-got-some-event-here…) of the task is repeating again and again. The desire is to make it as short and clear as possible. With decorators this could be written as:
@when Event.BUTTON_CLICK @on "button#add-new" :
{
this.select("#list").insert( new Element( "option", "new item") );
}
@when Event.SELECT_SELECTION_CHANGED @on "select#list" :
{
this.select("#delete-current").state.enabled = true;
}
...
This makes such sequence of blocks to look more like a table of records: when (event) on (where) (then do this). That is more declarative approach if you wish. This code is better maintainable I think.
@when and @on here are decorators of anonymous function that follow them. ( Sequence :{ ... } declares anonymous function in TIScript ).
Decorator in TIScript is an ordinary function with the name starting ‘@’ and at least one parameter. This first parameter is a reference to function that is being decorated. Decorator-function in its turn can dynamically create another function that will wrap call of original function.
Here is how our @when and @on decorators might look like:
// decorator '@when' - filters event by type
function @when(func, evtType)
{
return self.onControlEvent = function(evt)
{
if( evt.type == evtType)
return func.call(this,evt);
}
}
// decorator '@on' - filters evt.target by the selector
function @on(func, selector)
{
return function(evt)
{
if( evt.target.match(selector) ) // if target element matches
return func.call(this,evt); // the selector call the func.
}
}
As you may see both decorators simply create wrapper functions that filter the event using different criteria. Thus following statement:
@when Event.BUTTON_CLICK @on "button#add" :{...code...}
simply establishes chain of filters that ends up with the call of code that handles the event.
Syntax of decorators in TIScript is described here.