# Returns a char* starting at position `first_byte`
	#
	# WARNING: If you choose to use this service, be careful of the following.
	#
	# Strings and CString are *ideally* always allocated through a Garbage Collector.
	# Since the GC tracks the use of the pointer for the beginning of the char*, it may be
	# deallocated at any moment, rendering the pointer returned by this function invalid.
	# Any access to freed memory may very likely cause undefined behaviour or a crash.
	# (Failure to do so will most certainly result in long and painful debugging hours)
	#
	# The only safe use of this pointer is if it is ephemeral (e.g. read in a C function
	# then immediately return).
	#
	# As always, do not modify the content of the String in C code, if this is what you want
	# copy locally the char* as Nit Strings are immutable.
	fun fast_cstring: CString is abstract