Swift switch statement for matching substrings of a String - ios

Question

Im trying to ask for some values from a variable.
The variable is going to have the description of the weather and i want to ask for specific words in order to show different images (like a sun, rain or so)
The thing is i have code like this:
if self.descriptionWeather.description.rangeOfString("Clear") != nil
{
self.imageWeather.image = self.soleadoImage
}
if self.descriptionWeather.description.rangeOfString("rain") != nil
{
self.imageWeather.image = self.soleadoImage
}
if self.descriptionWeather.description.rangeOfString("broken clouds") != nil
{
self.imageWeather.image = self.nubladoImage
}
Because when i tried to add an "OR" condition xcode gives me some weird errors.
Is it possible to do a swich sentence with that? Or anyone knows how to do add an OR condition to the if clause?

Answer 1

I had a similar problem today and realized this question hasn't been updated since Swift 1! Here's how I solved it in Swift 4:
switch self.descriptionWeather.description {
case let str where str.contains("Clear"):
print("clear")
case let str where str.contains("rain"):
print("rain")
case let str where str.contains("broken clouds"):
print("broken clouds")
default:
break
}

Answer 2

Swift 5 Solution
func weatherImage(for identifier: String) -> UIImage? {
switch identifier {
case _ where identifier.contains("Clear"),
_ where identifier.contains("rain"):
return self.soleadoImage
case _ where identifier.contains("broken clouds"):
return self.nubladoImage
default: return nil
}
}

Answer 3

You can do this with a switch statement using value binding and a where clause. But convert the string to lowercase first!
var desc = "Going to be clear and bright tomorrow"
switch desc.lowercaseString as NSString {
case let x where x.rangeOfString("clear").length != 0:
println("clear")
case let x where x.rangeOfString("cloudy").length != 0:
println("cloudy")
default:
println("no match")
}
// prints "clear"

Answer 4

Swift language has two kinds of OR operators - the bitwise ones | (single vertical line), and the logical ones || (double vertical line). In this situation you need a logical OR:
if self.descriptionWeather.description.rangeOfString("Clear") != nil || self.descriptionWeather.description.rangeOfString("clear") != nil {
self.imageWeather.image = self.soleadoImage
}
Unlike Objective-C where you could get away with a bitwise OR in exchange for getting a slightly different run-time semantic, Swift requires a logical OR in the expression above.

Answer 5

If you do this a lot, you can implement a custom ~= operator that defines sub-string matching. It lends itself to this nice syntax:
switch "abcdefghi".substrings {
case "def": // calls `"def" ~= "abcdefghi".substrings`
print("Found substring: def")
case "some other potential substring":
print("Found \"some other potential substring\"")
default: print("No substring matches found")
}
Implementation:
import Foundation
public struct SubstringMatchSource {
private let wrapped: String
public init(wrapping wrapped: String) {
self.wrapped = wrapped
}
public func contains(_ substring: String) -> Bool {
return self.wrapped.contains(substring)
}
public static func ~= (substring: String, source: SubstringMatchSource) -> Bool {
return source.contains(substring)
}
}
extension String {
var substrings: SubstringMatchSource {
return SubstringMatchSource(wrapping: self)
}
}

Answer 6

I'd recommend using a dictionary instead, as a mapping between the substring you're searching for and the corresponding image:
func image(for weatherString: String) -> UIImage? {
let imageMapping = [
"Clear": self.soleadoImage,
"rain": self.soleadoImage,
"broken clouds": self.nubladoImage]
return imageMapping.first { weatherString.contains($0.key) }?.value
}
A dictionary gives you flexibility, adding new mappings is easy to do.

Answer 7

This link also describes overloading operator ~= which is actually used by the switch statement for matching cases to allow you to match regular expressions.