How to pass in an empty generator parameter?

Question

I have a method which takes a generator plus some additional parameters and returns a new generator:

function merge(\Generator $carry, array $additional)
{
    foreach ( $carry as $item ) {
        yield $item;
    }
    foreach ( $additional as $item ) {
        yield $item;
    }
}

The usual use case for this function is similar to this:

function source()
{
    for ( $i = 0; $i < 3; $i++ ) {
        yield $i;
    }
}

foreach ( merge(source(), [4, 5]) as $item ) {
    var_dump($item);
}

But the problem is that sometimes I need to pass empty source to the merge method. Ideally I would like to be able to do something like this:

merge(\Generator::getEmpty(), [4, 5]);

Which is exactly how I would do in C# (there is a IEnumerable<T>.Empty property). But I don't see any kind of empty generator in the manual.

I've managed to work around this (for now) by using this function:

function sourceEmpty()
{
    if ( false ) {
        yield;
    }
}

And this works. The code:

foreach ( merge(sourceEmpty(), [4, 5]) as $item ) {
    var_dump($item);
}

correctly outputs:

int(4)
int(5)

But this is obviously not an ideal solution. What would be the proper way of passing an empty generator to the merge method?

Answer 1

Bit late, but needed an empty generator myself, and realized creating one is actually quite easy...

function empty_generator(): Generator
{
    yield from [];
}

Don't know if that's better than using the EmptyIterator, but this way you get exactly the same type as non-empty generators at least.