# Write a map header for `len` keys/value pairs in the shortest possible MessagePack _map_ format
	#
	# After writing the header, clients should write the map data, alternating
	# between keys and values.
	#
	# Require: `len <= 0xFFFF_FFFF`
	fun write_msgpack_map(len: Int)
	do
		if len <= 0x0F then
			write_msgpack_fixmap len
		else if len <= 0xFFFF then
			write_msgpack_map16 len
		else if len <= 0xFFFF_FFFF then
			write_msgpack_map32 len
		else
			abort
		end
	end