为什么在Swift中不能在双精度元组上使用min（）？

Question

var coordinatesDouble = (Double(latitudeTextField.text!), Double(longitudeTextField.text!))

var boundingBoxLat: (Double, Double)
var boundingBoxLon: (Double, Double)

boundingBoxLat = (coordinatesDouble.0! - Constants.Flickr.SearchBBoxHalfHeight, coordinatesDouble.1! + Constants.Flickr.SearchBBoxHalfHeight)
boundingBoxLon = (coordinatesDouble.1! - Constants.Flickr.SearchBBoxHalfWidth, coordinatesDouble.1! + Constants.Flickr.SearchBBoxHalfWidth)

if min(boundingBoxLat) < -90.0 {

I am trying to use min() in an if statement, but am getting the error:

"Cannot invoke 'min' with an argument list of type (Double, Double)"

I thought this was specifically what this function was for. Am I missing something?

The equation for each double is one double being subtracted or added to another, resulting in a double. The if statement should then be determining if the lowest value in the tuple is lower than -90.0.

Answer 1

Am I missing something?

YES.

Please check this: SE-0029 Remove implicit tuple splat behavior from function applications

In the versions of Swift which include this SE-0029, Swift does not accept a tuple of two members as an actual parameter for function with two arguments .

(There is another overload for min , but it's irrelevant here.)

As commented by JAL, you need to pass two arguments to call min(_:_:) :

min(boundingBoxLat.0, boundingBoxLat.1)

---

Some addition.

I wonder if this line is really what you intend:

boundingBoxLat = (coordinatesDouble.0! - Constants.Flickr.SearchBBoxHalfHeight, coordinatesDouble.1! + Constants.Flickr.SearchBBoxHalfHeight)

It should be like this, no? (Please find the small difference in the latter half.):

boundingBoxLat = (coordinatesDouble.0! - Constants.Flickr.SearchBBoxHalfHeight, coordinatesDouble.0! + Constants.Flickr.SearchBBoxHalfHeight)

But it is not important my guess is right or not. Just you should know that this sort of code using tuples too much is less readable.

I recommend you to define your own structure to represent boundingBox :

struct CoordinateBox {
    var minLatitude: Double
    var maxLatitude: Double
    var minLongitude: Double
    var maxLongitude: Double

    init(latitude: Double, longitude: Double, height: Double, width: Double) {
        assert(height > 0.0)
        assert(width > 0.0)
        minLatitude = latitude - height
        maxLatitude = latitude + height
        minLongitude = longitude - width
        maxLongitude = longitude + width
    }
}

let boundingBox = CoordinateBox(latitude: Double(latitudeTextField.text ?? "") ?? 0,
                                longitude: Double(longitudeTextField.text ?? "") ?? 0,
                                height: Constants.Flickr.SearchBBoxHalfHeight,
                                width: Constants.Flickr.SearchBBoxHalfWidth)

if boundingBox.minLatitude < -90.0 {
    //...
}

You would never be confused with .0 s and .1 s.

Answer 2

A tuple can have different data types mixed together. You should use an array if all the datatypes are the same.