What is the preferred way to check if an optional has a value without using it?

Which of these is the ideal way to check if a value exists without caring exactly what its value is?

if let _ = flags[.showField] { showField() }

if flags[.showField] != nil { showField() }

In the first case, it seems more Swift-y to use if let _ = and futureproofs it (I can imagine a future where Apple says you must ask the optional if it has a value instead of comparing to nil). Additionally, if you come back to modify the code and find you need the value, you can just replace the _ with a name.

In the second case, it reads more naturally and is reflexive with if x == nil in a way that if let _ = is not.

Is one of these preferred over the other? If so, which and why?