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 optionTto valuex -
.has<T>()– Returns true iff optionTis set -
.unset<T>()– Removes the optionT -
.get<T>()– Gets a const-ref to the value of optionT -
.lookup<T>(x)– Gets a non-const-ref to optionT's value, initializing it toxif it was not set (xis 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 &)
rhs
Options const &
Options(Options &&)
rhs
Options &&
Operators
operator=(Options const &)
rhs
Options const &
Options &
operator=(Options &&)
rhs
Options &&
Options &
Functions
set(ValueTypeT< T >) &
Sets option T
to the value v
and returns a reference to *this
.
struct FooOption {
using Type = int;
};
auto opts = Options{};
opts.set<FooOption>(123);
v
ValueTypeT< T >
the value to set the option T
typename T
the option type
Options &
set(ValueTypeT< T >) &&
Sets option T
to the value v
and returns a reference to *this
.
struct FooOption {
using Type = int;
};
auto opts = Options{}.set<FooOption>(123);
v
ValueTypeT< T >
the value to set the option T
typename T
the option type
Options &&
has() const
Returns true IFF an option with type T
exists.
typename T
the option type
bool
unset()
Erases the option specified by the type T
.
typename T
the option type
void
get() const
Returns a reference to the value for T
, or a value-initialized default if T
was not set.
This method will always return a reference to a valid value of the correct type for option T
, whether or not T
has actually been set. Use has<T>()
to check whether or not the option has been set.
struct FooOption {
using Type = std::set<std::string>;
};
Options opts;
std::set<std::string> const& x = opts.get<FooOption>();
assert(x.empty());
assert(!x.has<FooOption>());
opts.set<FooOption>({"foo"});
assert(opts.get<FooOption>().size() == 1);
typename T
the option type
ValueTypeT< T > const &
lookup(ValueTypeT< T >)
Returns a reference to the value for option T
, setting the value to init_value
if necessary.
struct BigOption {
using Type = std::set<std::string>;
};
Options opts;
std::set<std::string>& x = opts.lookup<BigOption>();
assert(x.empty());
x.insert("foo");
opts.lookup<BigOption>().insert("bar");
assert(x.size() == 2);
value
ValueTypeT< T >
the initial value to use if T
is not set (optional)
typename T
the option type
ValueTypeT< T > &
