What does this two question mark mean?
swift
Solution
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.
Problem
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 ```