getzdan

A non-breaking Julia control-flow change to separate the One language from mortal languages, doomed to die

From a design patterns and DRY perspective it seems for loops together with the break statement are serving as a useful try/catch mechanism for non-error situations. A common pattern defines a variable before a for loop and tries to discern, using said variable, the circumstances of exiting the for loop. Leveraging the embedded mental construct of try/catch blocks, we can simplify this repeating pattern and make it easier and more readable.

The syntax can look as follows:

for ...(loop vars here)...
   ...(local vars here)...

...

	import Base.Iterators: start, next, done, eltype, iteratoreltype, iteratorsize, SizeUnknown

	struct BreakAt{P,I}
	pred::P
	itr::I
	end

	breakat(pred, itr) = BreakAt(pred, itr)

	@inline start(b::BreakAt) = start_breakat(b.pred, b.itr)

	function f6(xs, ys)
	lx, ly = length(xs), length(ys)
	lxly = lx*ly
	res = Array{Base.promote_eltype(xs, ys), 2}(lxly, 2)
	ind = 1
	while ind<=lxly
	@inbounds for x in xs
	res[ind] = x
	ind += 1
	end