On Monday, 4 February 2019 at 10:36:49 UTC, Ron Tarrant wrote:
On Sunday, 3 February 2019 at 18:53:10 UTC, Jacob Carlborg
wrote:
You don't need to make it so complicated. Here's a simpler
example:
Excellent. Thank you. Simple is best.
private __gshared auto instance_ = new DSingleton;
My understanding is that in D, this line effectively says: the
singleton is created at compile time and can't be changed,
ever. Is that a fair assessment?
No, it can.
´´´
class DSingleton
{
private __gshared auto instance_ = new DSingleton;
size_t state;
private this(){} // private to make sure no one else can
create an instance
static DSingleton instance() { return instance_; }
}
void main()
{
assert(DSingleton.instance.state == 0);
DSingleton.instance.state = 5;
assert(DSingleton.instance.state == 5);
}
´´´
private this() // private to make sure no one else can
create an instance
I've seen comments similar to this in several examples. When
you say "no one else" you're personifying callers?
To some extent...
And so this means: No caller outside the object? Which really
amounts to: Since no one INside the object WILL call this() and
no one OUTside CAN call this(), it won't ever get called.
I think, what is meant is: The class has to be placed alone in a
module so that no one outside the class (and the module) has any
direct access to object creation routine.
writeln(DSingleton.instance);
No '()' needed for the call to DSingleton.instance?
If it's called again from somewhere else, say from within an
object function several levels of scope away, it's called the
same way?
Yes. https://dlang.org/spec/function.html#optional-parenthesis
