+ # Returns a char* starting at position `index_from`
+ #
+ # WARNING: If you choose to use this service, be careful of the following.
+ #
+ # Strings and NativeString 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.
+ private fun fast_cstring: NativeString is abstract
+