On Saturday, 2 February 2019 at 16:56:45 UTC, Ron Tarrant wrote:
Hi guys,
I ran into another snag this morning while trying to implement
a singleton. I found all kinds of examples of singleton
definitions, but nothing about how to put them into practice.
Can someone show me a code example for how one would actually
use a singleton pattern in D? When I did the same thing in PHP,
it took me forever to wrap my brain around it, so I'm hoping to
get there a little faster this time.
Here's the singleton code I've been playing with:
class DSingleton
{
private:
// Cache instantiation flag in thread-local bool
// Thread local
static bool instantiated_;
// Thread global
__gshared DSingleton instance_;
this()
{
} // this()
public:
static DSingleton get()
{
if(!instantiated_)
{
synchronized(DSingleton.classinfo)
{
if(!instance_)
{
instance_ = new DSingleton();
writeln("creating");
}
instantiated_ = true;
}
}
else
{
writeln("not created");
}
return(instance_);
} // DSingleton()
} // class DSingleton
So, my big question is, do I instantiate like this:
DSingleton singleton = new DSingleton;
Or like this:
DSingleton singleton = singleton.get();
And subsequent calls would be...? The same? Using get() only?
Sorry, I should read the post fully before replying, my bad. You
access the singleton via the get() function whenever you need it.
It is static so there's no need to create a copy of the instance
in a "singleton" variable.
DSingleton singleton = new DSingleton; is bad. It bypasses all
the checks in the "get()" method to ensure it is a singleton and
outside the module where you defined DSingleton it won't compile.
bye,
norm
