Is it 'world-class' or 'world class'

[nicelyneurotic]

As in, 'a world-class city'. I'm leaning towards the hyphen. Is this right? Does it matter?

It's a world-class city, but the city is world class.

I think hyphen if used as an adjective, and not if not. 'The facilities there are world class' (though typing that, it doesn't seem like something anyone would say anyway!): 'it has world-class facilities'.

I'm just thinking of the nineteenth century/ nineteenth-century literature rule really.

YY to all the below. Though hyphens are dying out now and it's a race with apostrophes to the bottom.

Thanks all! Pedants is a lively place today

I cannot think of, or see any reason to hyphenate those two words.
They work well together and tell the whole story.
Why should they become linked in text or speech ?

They link them selves perfectly well and very well describe their purpose without the need for extra punctuation.