Module:Ustring

Copied from https://en.wikipedia.org/wiki/Module:Ustring.

The ustring library is intended to be a direct reimplementation of the standard String library, except that the methods operate on characters in UTF-8 encoded strings rather than bytes. Most functions will raise an error if the string is not valid UTF-8; exceptions are noted.

---

require('strict')
return setmetatable({}, {
	__index = function(t, k)
		local what = mw.ustring[k]
		if type(what) ~= "function" then
			return what
		end
		return function(frame)
			local fargs = frame.args
			local fargsused = { tag = true }
			local args = {}
			local str_i = 1
			while fargs['s' .. str_i] do
				fargsused['s' .. str_i] = true
				args[str_i] = fargs['s' .. str_i]
				str_i = str_i + 1
			end
			for i, v in ipairs(fargs) do
				fargsused[i] = true
				args[i + str_i - 1] = tonumber(v) or v:gsub("^\\", "", 1)
			end
			if not fargs.tag then
				return (what(unpack(args)))		-- Outside parens truncate to first result avoiding tail call
			end
			local tagargs = {}
			for x, y in pairs(fargs) do
				if not fargsused[x] then tagargs[x] = y end
			end
			return frame:extensionTag{name = fargs.tag, content = what(unpack(args)), args = tagargs}
		end
	end
})