Is it safe to force unwrap variables that have been optionally accessed in the same line of code?

someFunction(completion: { [weak self] in
    self?.variable = self!.otherVariable
})

Is this always safe? I access the optional self in the beginning of the statement, and personally I assume that the second part of this statement will never be executed if self is nil. Is this true? If self indeed is nil, the second part will never happen? And it will never happen that self could be 'nilled' during this single line of code?