FunctionParameter helper class

[marcusjhdon]

I've been porting a bunch of indicators from another platform to eSignal, and found many of them use the same or very similar input parameters. This meant there was a lot of duplicate, long-winded FunctionParameter code, so I decided to create a class to manage it, which I've attached.

To use it, you just create an instance of Params and then call addNumber(), addString(), addColor() or addBoolean() as required. Each function takes a name and title, plus an optional default value. All except addBoolean() also accepts an array of options (to create a drop-down list) as a fourth argument. In addition, I've created some predefined examples for common requirements, such as addLength(), addSource(), addSymbol() and addInterval(). Just for fun, I've given it a fluent interface, so you can chain them as show in the example below.

// Load libraries
var paramsLib = addLibrary("BionicTrader/Util/Params.efsLib");
var emaLib    = addLibrary("BionicTrader/MA/Ema.efsLib");

// Initialise global variables
var paramsObj;
var pricesObj;
var emaObj;

// Configure study
function preMain() {
	setStudyTitle("EMA");
	setCursorLabelName("EMA");
	setPriceStudy(true);
	setDefaultBarFgColor(Color.RGB(0, 148, 255));
	setPlotType(PLOTTYPE_LINE);
	setDefaultBarThickness(1);
	askForInput();

	// Setup user-defined input parameters
	paramsObj = new paramsLib.Params();
	paramsObj.addLength(20).addSource().addSymbol().addInterval();
	paramsObj.addNumber('offset', 'Offset', 0, null, 0);
	paramsObj.addBoolean('params', 'Show Parameters', false);
}

// Get indicator value
function main(length, source, symbol, interval, offset, params) {
	length   = length   || paramsObj.getDefault('length');
	source   = source   || paramsObj.getDefault('source');
	symbol   = symbol   || paramsObj.getDefault('symbol');
	interval = interval || paramsObj.getDefault('interval');
	offset   = offset   || paramsObj.getDefault('offset');
	if (params === undefined) params = paramsObj.getDefault('params');
	
	// Instantiate library classes etc on first call
	if (emaObj === undefined) {
		pricesObj = paramsObj.getPrices(source, symbol, interval);
		emaObj = new emaLib.Ema(length);
		setShowTitleParameters(params);
	}
	
	// Return new value
	return emaObj.getNext(pricesObj.getValue(offset));
}

I've no idea how many people are interesting in this sort of thing, so please let me know if you think it's worth me sharing stuff like this in future

[waynecd]

I for one found it very useful for the techniques (like understanding the use of "this" keyword) but I can't run/test it all without the "EMA.efsLib".
I will comment the EMA... lines out to play with how the utility class was created but would like the EMA.efsLib if possible.

Thanks,

Wayne