Fixing "Ambiguous reference to member when using ceil or round"

Swift version: 5.1

Paul Hudson    @twostraws    May 28th 2019

If you've ever come across the error message "No 'ceil' candidates produce the expected contextual result type 'Int'" – which can happen with calls to ceil(), floor(), and round() – it's usually down to Swift being unable to satisfy type requirements you have asked for.

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 c: Int = ceil(a)

If you need c to be an integer, the solution is to convert the return value of ceil() to be an integer, like this:

let c = Int(ceil(a))

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

Available from iOS 7.0

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