Re: Filtering Iterator

[Kevin Martin <kev82@...>]

On 22 Dec 2012, at 16:19, joao lobato wrote:

> However, all that packing and unpacking is bound to have a performance
> hit.

I hadn't considered that, as in almost all cases there is only one return value. I will think about your suggestions, thanks.

On 22 Dec 2012, at 16:34, Dirk Laurie wrote:

> Is there a reason why the obvious Lua code is inefficient, obscure
> or not applicable?

I want to write the following code:

for a in carer:availBlocks() do
	--do something with a
end

I do not want to write:

for a in carer:toProblem():availBlocks() do if carer:id() == a:carer():id() then
	--do something with a
end 

Without an iterator filter, the only way I can think to implement, carer.availBlocks is to use a temporary table:

function carer_mt.availBlocks()
	local t = {}
	for b in self:toProblem():availBlocks() do
		if b:carer():id() == self:id() then
			t[b] = true
		end
	end
	return pairs(t)
end

Sometimes there are 1000s of elements and repeatedly creating the temporary table for every time I iterate seems like a bad idea.

Thanks,
Kevin