singleton

Overview

The singleton template class ensures that only one instance of a class is created. It uses a static pointer, initialized to nullptr and to check if an instance exists. The instance method returns a reference to the single instance, ensuring controlled access. This design supports without default constructors and provides a safe way to implement the singleton pattern.

Usage

Preconditions	Make sure to include the appropriate library header for singleton.
Assumptions	The constructor of the class must pass its pointer to the base class singleton in order to instantiate it.
Usage guidance	Once instantiated, always use the instance() method to access the object.

Example

The following example shows the usage of singleton using structure:

struct Foo : ::estd::singleton<Foo>
{
    // initialize singleton instance
    Foo() : ::estd::singleton<Foo>(*this), _v(0) {}

    int32_t _v; // internal variable
};

TEST(Singleton, TestInstance)
{
    // check Foo is not instantiated
    ASSERT_FALSE(Foo::instantiated());
    Foo f;                            // instance
    ASSERT_EQ(&f, &Foo::instance());  // check the singleton instance's match
    ASSERT_TRUE(Foo::instantiated()); // verify Foo is instantiated
}