Update – Sep 2019: PECL memcached extension v3.1.0 and above support PHP 7.3
Just a note that the PECL memcached extension doesn’t work with PHP 7.3 yet, you need to stay on PHP 7.2.
This is the error I got when trying to running sudo perl install memcached (along with several sasl deprecation warnings):
/private/tmp/pear/install/memcached/php_memcached.c:1284:20: error: expression is not assignable
NB: Also, don’t get memcache and memcached mixed up when searching extensions.