guard

示例代码

func peripheralViewModel(at row: Int) -> SILDiscoveredPeripheralDisplayDataViewModel? {
        guard row < discoveredPeripheralsViewModels.count else { return nil }
        return discoveredPeripheralsViewModels[row]
    }

说明：把 guard 当作是断言会更好理解

• 如果断言为yes，则继续往下执行，如果断言为no，则走else里面的代码

if let

示例代码1

if let firstIndex = firstIndexOfReplacement(device: peripheral) {
    let replacement = replaceViewModels[firstIndex]
    if (allDiscoveredPeripheralsViewModels[index].discoveredPeripheral.isFavourite) {
        replacement.discoveredPeripheral.isFavourite = true
    }
    allDiscoveredPeripheralsViewModels[index] = replacement
}

说明

• if let 主要是判断后面的可选项类型是否有值，如果有值就将该值赋值给这个常量

示例代码2

if let discoveredPeripheral = peripheralViewModel.discoveredPeripheral,
    discoveredPeripheral.isConnectable,
    centralManager.canConnect(to: discoveredPeripheral) {
    centralManager.connect(to: discoveredPeripheral)
    isConnecting.updateValue(true, forKey: discoveredPeripheral.peripheral!)
} else {
    isConnecting.updateValue(false, forKey: peripheralViewModel.discoveredPeripheral.peripheral!)
}

说明

• if let 后面可以有多个需要判断的条件