/// <summary>
/// Creates a new Singleton.
/// </summary>
/// <param name="getInstanceFunction">A function to create an instance of the given type. If null will be set to default constructor of this type.</param>
/// <param name="initializeDirectly">Shall the Singleton be directly initialized upfront?</param>
/// <exception cref="MissingMethodException">Throws a MissingMethodException when no getInstanceFunction is given and the type does not contain a default constructor and is no ValueType.</exception>
public Singleton(Func <T> getInstanceFunction = null, bool initializeDirectly = false)
{
_instance = default(T);
_getInstance = getInstanceFunction;
if (_getInstance == null)
{
var ctor = typeof(T).GetConstructor(Type.EmptyTypes);
if (ctor == null)
{
if (typeof(T).IsValueType)
{
_initialized = true; // has already been initialized in the first line to default(T).
return;
}
else
{
throw new MissingMethodException("There is no empty constructor defined for this type. Please implement an empty constructor or provide a initialization function.");
}
}
else // just for code clarity.
{
// Create method to call the empty constructor for the given type.
// See https://stackoverflow.com/questions/10593630/create-delegate-from-constructor
DynamicMethod dynamic = new DynamicMethod(string.Empty, typeof(T), Type.EmptyTypes, typeof(T));
ILGenerator il = dynamic.GetILGenerator();
il.DeclareLocal(typeof(T));
il.Emit(OpCodes.Newobj, ctor);
il.Emit(OpCodes.Stloc_0);
il.Emit(OpCodes.Ldloc_0);
il.Emit(OpCodes.Ret);
_getInstance = (Func <T>)dynamic.CreateDelegate(typeof(Func <T>));
}
}
if (initializeDirectly)
{
if (!_initialized)
{
_instance = _getInstance();
}
_initialized = true;
}
else
{
_singletonLock = new UsableMutexSlim();
}
}
