#### io_service::has_service

Determine if an io_service contains a specified service type.

    template<
        typename Service>
    friend bool has_service(
        io_service & ios);

This function is used to determine whether the io_service contains a service object corresponding to the given service type.

###### Parameters

ios

  The io_service object that owns the service.

###### Return Value

A boolean indicating whether the io_service contains the service.