swift – 无法找到 – 的重载,尽管所有参数都是double

let x = Double(pr)
let x2 : Double = pow(x, 2.0)
let x3 : Double = pow(x, 3.0)
let x4 : Double = pow(x, 4.0)
let r = CGFloat( 4.8 * x4 - 10.4 * x3 + 5.7 * x2 + 1.05 * x + 0.95 )
let g = CGFloat( 4.8 * x4 - 8.8 * x3  + 3.3 * x2 + 1.65 * x + 0.0 )
let b = CGFloat(0.0)
let color = UIColor(red: r, green: g, blue: b, alpha: 1.0)
return color.CGColor

没有太多要解释的,它只是抛出编译器的错误：“找不到’ – ‘接受提供的参数的重载.此外,我尝试在各处使用浮点类型的powf(x,2). pr是函数CGFloat类型参数.这是截图：.

谢谢！

note: expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions
let g = CGFloat( 4.8 * x4 - 8.8 * x3  + 3.3 * x2 + 1.65 * x + 0.0 )
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

作为解决方法,您可以首先将表达式分配给临时变量：

let tmp = 4.8 * x4 - 10.4 * x3 + 5.7 * x2 + 1.05 * x + 0.95
let r = CGFloat( tmp )

备注：在给定点评估多项式的​​更有效方法
是Horner’s method：

let tmp = (((4.8 * x - 10.4) * x + 5.7) * x + 1.05) * x + 0.95

你不必计算x的各种权力.