mutable keyword

mutable_practice.cpp

#include <iostream>
using std::cout;
using std::endl;

static int SomeDataSource = 100;

class LazyFetching
{
public:
	LazyFetching() : m_pDataSource( nullptr ) {}
	int GetData() const;
private:
	mutable int* m_pDataSource;
};

int LazyFetching::GetData() const
{
	if( m_pDataSource == nullptr )
	{
		m_pDataSource = &SomeDataSource;
	}
	
	return *m_pDataSource;
}

int main()
{
	LazyFetching obj;
	cout << obj.GetData() << endl;
	
	return 0;
}