The Singleton class is designed to be subclassed by clients for use in embedded systems without a dynamic memory allocator. The typical use case is for writing a class to represent a piece of hardware of which there can only be one (e.g. a motor, sensor, or other piece of physical hardware).
To use the Singleton class, simply subclass it as follows:
class SpecificSingleton : public Singleton<SpecificSingleton>
{
public:
SpecificSingleton() : someData_(42) {}
~SpecificSingleton() {}
private:
int someData_;
};
and then you can get a reference to your singleton like this:
SpecificSingleton & a = SpecificSingleton::Instance();
The class is implemented as headers only, so to use it simply add Singleton.h
and Singleton_priv.h to the include path of your project. No libraries need
to be built or installed. make install will install these headers to your
system.
That's all there is to it!
A couple of simple tests are implemented with googletest. For some reason googletest still uses subversion, so I had to monkey around a bit in order to make googletest into a git submodule. I basically followed the advice given here. In order to clone and build the Singleton repository, repeat the following incantation
$ git clone git://github.com/hazelnusse/Singleton.git
$ cd Singleton
$ git submodule init
$ git submodule update
$ mkdir build
$ cd build
$ cmake .. # or: cmake-gui ..
$ make # doesn't do anything if you disabled tests
$ make test # doesn't do anything if you disabled tests
$ make install # installs headers to /usr/local/include by default
-
Make Singleton constructor allow for finite numbers of unique Singletons. For example, if you have two physical pieces of hardware, it would be useful to be able to do
SpecificSingleton & a = SpecificSingleton::Instance(0); SpecificSingleton & b = SpecificSingleton::Instance(1);It might be useful to allow extra arguments to the Instance() method, in which case variadic templates might work.