swift可选链

private func displayOne(_ annotationType: AnyClass) {
        let annotation = allAnnotations?.first { (annotation) -> Bool in
            return annotation.isKind(of: annotationType)
        }
        
        if let oneAnnotation = annotation {
            displayedAnnotations = [oneAnnotation]
        } else {
            displayedAnnotations = []
        }
    }

去掉？报错为：

Value of optional type '[MKAnnotation]?' must be unwrapped to refer to member 'first' of wrapped base type '[MKAnnotation]'

提示解决方案：

Chain the optional using '?' to access member 'first' only for non-'nil' base values

Force-unwrap using '!' to abort execution if the optional value contains 'nil'

结论：

想让解包为空的时候优雅结束用“?” 想让为空时直接终止程序用“!”