Merge pull request #11 from svermeulen/sverm/infinite-loop-fix

Fix for the very common infinite loop issue, when forgetting to call getIterator

src/lazylualinq.lua

@@ -160,7 +160,13 @@ end
 -- as other functions that return a sequence.
 function linq.factory(fac)
 	return setmetatable({}, { 
-		__call = fac, 
+		__call = function(self, ...)
+			local numArgs = select('#', ...)
+			if numArgs > 0 then
+				error("Invalid use of lazylualinq sequence.  Did you forget to call it (or getIterator) before using it inside a for loop?", 2)
+			end
+			return fac(self)
+		end,
 		__index = linq,
 		__len = function(self) 
 			return self:count()

test/intermediate/for_loop.lua

@@ -0,0 +1,33 @@
+
+describe("for loop usage", function()
+	local linq = require("lazylualinq")
+
+	it("throws error when getIterator is not called", function()
+		local seq = linq { 1, 2, 3 }
+
+        assert.has_error(function() 
+            for _x in seq do
+            end
+        end)
+
+        local items = {}
+        for x in seq() do
+            table.insert(items, x)
+        end
+
+		assert.is_same(#items, 3)
+		assert.is_same(items[1], 1)
+		assert.is_same(items[2], 2)
+		assert.is_same(items[3], 3)
+
+        items = {}
+        for x in seq:getIterator() do
+            table.insert(items, x)
+        end
+
+		assert.is_same(#items, 3)
+		assert.is_same(items[1], 1)
+		assert.is_same(items[2], 2)
+		assert.is_same(items[3], 3)
+	end)
+end)