Function parse_cidr 

pub fn parse_cidr<C, AP>(
    s: &str,
    address_parser: AP,
) -> Result<C, NetworkParseError>
where
    C: Cidr,
    AP: Fn(&str) -> Result<C::Address, AddrParseError>,

Parse Cidr with custom address parser

If a ‘/’ is found, parse trailing number as prefix length and leading address with address_parser. Otherwise parse address_parser and treat as host (maximum prefix length).