Swift 3 (Xcode 8)
```swift
func matches(for regex: String, in text: String) -> [String] {

    do {
        let regex = try NSRegularExpression(pattern: regex)
        let nsString = text as NSString
        let results = regex.matches(in: text, range: NSRange(location: 0, length: nsString.length))
        return results.map { nsString.substring(with: $0.range)}
    } catch let error {
        print("invalid regex: \(error.localizedDescription)")
        return []
    }
}
```
Example:

```swift
let string = "🇩🇪€4€9"
let matched = matches(for: "[0-9]", in: string)
print(matched)
// ["4", "9"]
```

---
As of Swift 4 (Xcode 9), the Swift standard library provides functions to convert between Range<String.Index> and NSRange.

```
func matches(for regex: String, in text: String) -> [String] {

    do {
        let regex = try NSRegularExpression(pattern: regex)
        let results = regex.matches(in: text,
                                    range: NSRange(text.startIndex..., in: text))
        return results.map {
            String(text[Range($0.range, in: text)!])
        }
    } catch let error {
        print("invalid regex: \(error.localizedDescription)")
        return []
    }
}
```

Example:

```
let string = "🇩🇪€4€9"
let matched = matches(for: "[0-9]", in: string)
print(matched)
// ["4", "9"]
```

Note: The forced unwrap Range($0.range, in: text)! is safe because the NSRange refers to a substring of the given string text. However, if you want to avoid it then use

```
        return results.flatMap {
            Range($0.range, in: text).map { String(text[$0]) }
        }
```

extension String
{
    func hashtags() -> [String]
    {
        if let regex = try? NSRegularExpression(pattern: "#[a-z0-9]+", options: .caseInsensitive)
        {
            let string = self as NSString

            return regex.matches(in: self, options: [], range: NSRange(location: 0, length: string.length)).map {
                string.substring(with: $0.range).replacingOccurrences(of: "#", with: "").lowercased()
            }
        }

        return []
    }
}