使用ceil或round时对成员的模糊引用

Question

I am just trying to use the ceil or round functions in Swift but am getting a compile time error:

Ambiguous reference to member 'ceil'.

I have already imported the Foundation and UIKit modules. I have tried to compile it with and without the import statements but no luck. Does anyone one have any idea what I am doing wrong? my code is as follow;

import UIKit

@IBDesignable class LineGraphView: GraphView {
override func setMaxYAxis() {
            self.maxYAxis = ceil(yAxisValue.maxElement())

    }
   }

Answer 1

This problem occurs for something that might seem strange at first, but it's easily resolved.

Put simply, you might think calling ceil() rounds a floating-point number up to its nearest integer, but actually it doesn't return an integer at all: if you give it a Float it returns a Float , and if you give it a Double it returns a Double .

So, this code works because c ends up being a Double :

let a = 0.5
let c = ceil(a)

…whereas this code causes your exact issue because it tries to force a Double into an Int without a typecast:

let a = 0.5
let c: Int = ceil(a)

The solution is to convert the return value of ceil() to be an integer, like this:

let a = 0.5
let c = Int(ceil(a))

The same is true of the round() function, so you'd need the same solution.

Answer 2

Depending on the scope of where you call ceil , you may need to explicitly call Darwin 's ceil function (deep in a closure, etc). Darwin is imported through Foundation , which is imported by UIKit .

let myFloat = 5.9
let myCeil = Darwin.ceil(myFloat) // 6

On linux, Glibc is used in place of Darwin for C-level API access. You would have to explicitly import Glibc and call Glibc.ceil(myFloat) instead of using Darwin .