add gs

RCCService2018/content/LuaPackages/RoactImpl/oneChild.lua

@@ -0,0 +1,28 @@
+--[[
+	Utility to retrieve one child out the children passed to a component.
+
+	If passed nil or an empty table, will return nil.
+
+	Throws an error if passed more than one child, but can be passed zero.
+]]
+local function oneChild(children)
+	if not children then
+		return
+	end
+
+	local key, child = next(children)
+
+	if not child then
+		return
+	end
+
+	local after = next(children, key)
+
+	if after then
+		error("Expected at most child, had more than one child.", 2)
+	end
+
+	return child
+end
+
+return oneChild