What does this two question mark mean?

liyansong

I met with this code, and I could not figure out what does this two question marks mean?

the Definition of this variable looks like following:

var featureImageSizeOptional: CGSize?   

The code that makes me confused is:

let featureImageSize = featureImageSizeOptional ?? CGSizeZero
Todd Agulnick

It's the coalescing operator. It returns the first expression (featureImageSizeOptional) if it's non-nil. If the first expression is nil, the operator returns the second expression (CGSizeZero).

See the Language Guide for more info.

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