Optional

A dp::optional, copying std::optional is a type which either contains a value or does not. It maintains a well-defined state in both situations, performs no heap allocation, and does not construct the held object until it needs to. Helper instance dp::nullopt can be used to represent an empty optional.

Copy operations on a dp::optional maintain the strong exception guarantee. Optionals may not contain reference types, or instances of dp::nullopt_t

Functions

operator* operator->	Access held value, without checking
operator bool has_value	Check if the optional holds a value
value	Returns the held value, with checking
value_or	Returns the held value if there is one, and the parameter if not
swap	Swaps the values and statuses of two optionals
reset	Destroys any held value
operator== operator!= operator< operator<= operator> operator>=	Compares the held values of two optionals
make_optional	Creates an optional object

Sample Code

#include "cpp98/optional.h"

dp::optional<std::string> get_name(){
    DB_query.add("SELECT [Name] FROM Foo WHERE Bar");
    DB_query.open();
    if(DB_query.empty()) return dp::nullopt;   //Return an empty optional to signify that the name was not found
    else return DB_query.get_value();
}

int main(){
    dp::optional<std::string> name = get_name();

    Print("The name in the database is " + name.value_or("not found")); //Prints the name if we got it from the function, or "not found" if not.
}