@ path  std::string const &
@ count int

In function signatures the type is used as written: std::string NotFoundStr( std::string const & path, int count ).

In generated classes (streamable, exception) each parameter is stored by value, as std::decay_t< type >, in a member member_<name> — so an exception built from a std::string const & owns its string. Each has a getter with the parameter's name:

std::decay_t< std::string const & > const &path( ) const;   // std::string const &

A class constructor with exactly one parameter is explicit.

In the text a parameter is used through a macro, {$path}. A parameter no language uses is allowed (data the class carries); one that some languages use and others do not is a warning.