Singleton

Allows creation of a singleton, with deterministic construction and destruction.

etl::singleton<typename T>

T The type to use as a singleton.

Before create Is called, the singleton is in the invalid state.

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Static functions

C++03 and below.

static void create()

Creates the singleton. Default constructs the instance.

Sets the singleton to the valid state.

Only the first call to create is effective.

Must be called before any calls to instance().

template <typename T1>

static void create(const T1& p1)

Construct from 1 parameter.

template <typename T1, typename T2>

static void create(const T1& p1, const T2& p2)

Construct from 2 parameters.

template <typename T1, typename T2, typename T3>

static void create(const T1& p1, const T2& p2, const T3& p3)

Construct from 3 parameters.

template <typename T1, typename T2, typename T3, typename T4>

static void create(const T1& p1, const T2& p2, const T3& p3, const T4& p4)

Construct from 4 parameters.

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C++11 and above.

template <typename... TArgs>

static void create(TArgs&&... args)

Creates the singleton and constructs the type using the supplied parameters.

Sets the singleton to the valid state.

Only the first successful call to create is effective. Does nothing if the singleton is already valid.

Must be called before any calls to instance().

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static T& instance()

Returns a reference to the one instance of T.

Asserts an etl::singleton_not_created if create has not been called.

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static void destroy()

Calls the destructor of the instance.

Sets the singleton to the invalid state.

Only the first successful call to destroy is effective. Does nothing if the singleton is already invalid.

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static bool is_valid()

Returns true if the instance is valid.

Returns false before create and after destroy are called.

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Example

class MyType;

using MySingleton = etl::singleton<MyType>;

bool is_valid;

is_valid = MySingleton::is_valid(); // false

MyType& mt1 = MySingleton::instance(); // Raises ETL_ASSERT etl::singleton_not_created

MySingleton::create(1, "Hello World"); // Construct with parameters

is_valid = MySingleton::is_valid(); // true

MyType& mt2 = MySingleton::instance(); // Get the instance

is_valid = MySingleton::is_valid(); // true

MySingleton::destroy(); // Destruct the instance

is_valid = MySingleton::is_valid(); // false

singleton.h