Swift moveBy方法不会接受CGFloat参数

我在let moveBy函数中的x值不断出现此错误：

无法将“CGFloat”类型的值转换为预期的参数类型“CGVector”

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距离是CGFloat，moveBy方法中的x参数是CGFloat。不确定它为什么不起作用。

这一行缺少一个右括号：

if gameStarted == false {
    let spawn = SKAction.run({
        () in

        self.createPlatforms()

    })

    let delay = SKAction.wait(forDuration: 1.5)
    let spawnDelay = SKAction.sequence([spawn, delay])
    let spawnDelayForever = SKAction.repeatForever(spawnDelay)
    self.run(spawnDelayForever)

    let distance = CGFloat(self.frame.width + platformPair.frame.width)
    let movePlatforms = SKAction.moveBy(x: -distance, y: 0, duration: TimeInterval(0.01 * Double(distance))
    let removePlatforms = SKAction.removeFromParent()
    moveAndRemove = SKAction.sequence([movePlatforms, removePlatforms])

    player.physicsBody?.velocity = CGVector(dx: 0, dy: 0)
    player.physicsBody?.applyImpulse(CGVector(dx: 0,dy: 150))

} else {
    player.physicsBody?.velocity = CGVector(dx: 0, dy: 0)
    player.physicsBody?.applyImpulse(CGVector(dx: 0,dy: 150))
}

let movePlatforms = SKAction.moveBy(x: -distance, y: 0, duration: TimeInterval(0.01 * Double(distance)))