Class Options (2.20.0-rc)

A class that holds option structs indexed by their type.

An "Option" is any struct that has a public Type member typedef. By convention they are named like "FooOption". Each library (e.g., spanner, storage) may define their own set of options. Additionally, there are common options defined that many libraries may use. All these options may be set in a single Options instance, and each library will look at the options that it needs.

Here's an overview of this class's interface, but see the method documentation below for details.

  • .set<T>(x)– Sets the option T to value x
  • .has<T>()– Returns true iff option T is set
  • .unset<T>()– Removes the option T
  • .get<T>()– Gets a const-ref to the value of option T
  • .lookup<T>(x)– Gets a non-const-ref to option T's value, initializing it to x if it was not set (x is optional).
Example:
struct FooOption {
  using Type = int;
};
struct BarOption {
  using Type = std::set<std::string>;
};
...
Options opts;

assert(opts.get<FooOption>() == 0);
opts.set<FooOption>(42);
assert(opts.get<FooOption>() == 42);

// Inserts two elements directly into the BarOption's std::set.
opts.lookup<BarOption>().insert("hello");
opts.lookup<BarOption>().insert("world");

std::set<std::string> const& bar = opts.get<BarOption>();
assert(bar == std::set<std::string>{"hello", "world"});

Constructors

Options()

Constructs an empty instance.

Options(Options const &)

Parameter
NameDescription
rhs Options const &

Options(Options &&)

Parameter
NameDescription
rhs Options &&

Operators

operator=(Options const &)