multiple binding

gistfile1.d

IProperty firstName, lastName, fullName;

// fetch properties from widgets.

auto converter = (Variant firstName, Variant lastName){
	return Variant(firstName ~ " " ~ lastName);
};

fullName.pipeFrom(cast(Variant delegate(Variant[]...))converter, firstName, lastName);

template isVariant(T)
{
	enum isVariant = is(T == Variant);
}

import std.conv;
alias ExtractValues(Properties...) = ExtractValuesImpl!(0, Properties);

template ExtractValuesImpl(uint index, Properties...)
{
	pragma(msg, (Properties).length);

	static if(Properties.length > 1)
		enum ExtractValuesImpl = "sources[" ~ to!string(index) ~ "].value, " ~ ExtractValuesImpl!(index + 1, Properties[1..$]);
	else
		enum ExtractValuesImpl = "sources[" ~ to!string(index) ~ "].value";
}

import std.algorithm;
import std.range;
import std.traits;
import std.typetuple;
/// creates one-way binding from multiple to one property
/// destination.pipeFrom((Variant a, Variant b)=> a+b, num1, num2);
void pipeFrom(ConverterType, P ...)(IProperty dest, ConverterType converter, P sources)
if  (is(ReturnType!ConverterType == Variant) &&
	(ParameterTypeTuple!ConverterType).length == P.length &&
	is(NoDuplicates!(ParameterTypeTuple!ConverterType) == TypeTuple!Variant) &&
	is(NoDuplicates!P == TypeTuple!IProperty))
{
	auto handler = (FlexibleObject obj, Variant value){
		dest.value = mixin("converter("~ExtractValues!sources~")");
	};

	foreach(index, IProperty source; sources)
	{
		source.valueChanged.connect(handler);
	}

	dest.value = mixin("converter("~ExtractValues!sources~")");
}