A class is a service if it is publicly and unambiguously
derived from execution_context::service
, or if it is publicly
and unambiguously derived from another service. For a service S
,
S::key_type
shall be valid and denote a type (C++Std [temp.deduct]),
is_base_of_v<typename S::key_type, S>
shall be true
,
and S
shall satisfy the Destructible
requirements
(C++Std [destructible]).
The first parameter of all service constructors shall be an lvalue reference
to execution_context
. This parameter denotes the execution_context
object that represents a set of services, of which the service object will
be a member. [Note: These constructors may be called
by the make_service
function. —end note]
A service shall provide an explicit constructor with a single parameter of
lvalue reference to execution_context
. [Note:
This constructor may be called by the use_service
function.
—end note]
class my_service : public execution_context::service { public: typedef my_service key_type; explicit my_service(execution_context& ctx); my_service(execution_context& ctx, int some_value); private: virtual void shutdown() noexcept override; ... };
A service's shutdown
member function shall destroy all copies
of user-defined function objects that are held by the service.