The class templatescope_success is a general-purpose scope guard intended to call its exit function when a scope is normally exited.

scope_success is notCopyConstructible,CopyAssignable orMoveAssignable, however, it may beMoveConstructible ifEF meets some requirements, which permits wrapping ascope_success into another object.

Ascope_success may be either active, i.e. calls its exit function on destruction, or inactive, i.e. does nothing on destruction. Ascope_success is active after constructed from an exit function.

Ascope_success can become inactive by callingrelease() on it either manually or automatically (by the move constructor). An inactivescope_success may also be obtained by initializing with another inactivescope_success. Once ascope_success is inactive, it cannot become active again.

Ascope_success effectively holds anEF and abool flag indicating if it is active, alongwith a counter of uncaught exceptions used for detecting whether the destructor is called during stack unwinding.

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[edit]Notes

Constructing ascope_success of dynamic storage duration might lead to unexpected behavior.

Constructing ascope_success is constructed from anotherscope_success created in a different thread might also lead to unexpected behavior since the count of uncaught exceptions obtained in different threads may be compared during the destruction.

If theEF stored in ascope_success object refers to a local variable of the function where it is defined, e.g., as a lambda capturing the variable by reference, and that variable is used as a return operand in that function, that variable might have already been returned when thescope_success's destructor executes, calling the exit function. This can lead to surprising behavior.

[edit]Example

#include <iostream>#include <cstdlib>#include <string_view>#include <experimental/scope> void print_exit_status(std::string_view name,bool exit_status,bool did_throw){std::cout<< name<<":\n";std::cout<<"  Throwed exception  "<<(did_throw?"yes":"no")<<"\n";std::cout<<"  Exit status        "<<(exit_status?"finished":"pending")<<"\n\n";} // Randomly throw an exception (50% chance)void maybe_throw(){if(std::rand()>=RAND_MAX/2)throwstd::exception{};} int main(){bool exit_status{false}, did_throw{false}; // Manual handling at "end of scope"try{    maybe_throw();    exit_status=true;}catch(...){ did_throw=true;}  print_exit_status("Manual handling", exit_status, did_throw); // Using scope_exit: runs on scope exit (success or exception)  exit_status= did_throw=false;try{auto guard= std::experimental::scope_exit{[&]{ exit_status=true;}};    maybe_throw();}catch(...){ did_throw=true;}  print_exit_status("scope_exit", exit_status, did_throw); // Using scope_fail: runs only if an exception occurs  exit_status= did_throw=false;try{auto guard= std::experimental::scope_fail{[&]{ exit_status=true;}};    maybe_throw();}catch(...){ did_throw=true;}  print_exit_status("scope_fail", exit_status, did_throw); // Using scope_success: runs only if no exception occurs  exit_status= did_throw=false;try{auto guard= std::experimental::scope_success{[&]{ exit_status=true;}};    maybe_throw();}catch(...){ did_throw=true;}  print_exit_status("scope_success", exit_status, did_throw);}

Manual handling:  Throwed exception  yes  Exit status        pending scope_exit:  Throwed exception  no  Exit status        finished scope_fail:  Throwed exception  yes  Exit status        finished scope_success:  Throwed exception  yes  Exit status        pending

[edit]See also

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