Class Options (2.46.0-rc)
A class that holds option structs indexed by their type.
An "Option" is any struct that has a publicType 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 singleOptions 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 &)
| Parameter | |
|---|---|
| Name | Description |
rhs | Options const & |
Options(Options &&)
| Parameter | |
|---|---|
| Name | Description |
rhs | Options && |
Operators
operator=(Options const &)
| Parameter | |
|---|---|
| Name | Description |
rhs | Options const & |
| Returns | |
|---|---|
| Type | Description |
Options & | |
operator=(Options &&)
| Parameter | |
|---|---|
| Name | Description |
rhs | Options && |
| Returns | |
|---|---|
| Type | Description |
Options & | |
Functions
set(ValueTypeT< T >) &
Sets optionT to the valuev and returns a reference to*this.
struct FooOption { using Type = int;};auto opts = Options{};opts.set<FooOption>(123);| Parameters | |
|---|---|
| Name | Description |
v | ValueTypeT< T >the value to set the option T |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
Options & | |
set(ValueTypeT< T >) &&
Sets optionT to the valuev and returns a reference to*this.
struct FooOption { using Type = int;};auto opts = Options{}.set<FooOption>(123);| Parameters | |
|---|---|
| Name | Description |
v | ValueTypeT< T >the value to set the option T |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
Options && | |
has() const
Returns true IFF an option with typeT exists.
| Parameter | |
|---|---|
| Name | Description |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
bool | |
unset()
Erases the option specified by the typeT.
| Parameter | |
|---|---|
| Name | Description |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
void | |
get() const
Returns a reference to the value forT, or a value-initialized default ifT was not set.
This method will always return a reference to a valid value of the correct type for optionT, whether or notT has actually been set. Usehas<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);| Parameter | |
|---|---|
| Name | Description |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
ValueTypeT< T > const & | |
lookup(ValueTypeT< T >)
Returns a reference to the value for optionT, setting the value toinit_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);| Parameters | |
|---|---|
| Name | Description |
value | ValueTypeT< T >the initial value to use if |
typename T | the option type |
| Returns | |
|---|---|
| Type | Description |
ValueTypeT< T > & | |
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Last updated 2025-12-17 UTC.