Configuration.swift

struct Configuration: BooleanType {
    
    private let isActiveConfiguration: Bool
    
    // Extend to your heart's content, e.g. size classes
    init(idiom: UIUserInterfaceIdiom? = nil, os: NSOperatingSystemVersion? = nil) {
        var configuration = true
        if let idiom = idiom {
            configuration = idiom == UIDevice.currentDevice().userInterfaceIdiom
        }
        if let os = os {
            configuration = configuration && NSProcessInfo().operatingSystemVersion == os
        }
        isActiveConfiguration = configuration
    }
    
    var boolValue: Bool {
        return isActiveConfiguration
    }
    
}

extension NSOperatingSystemVersion: Equatable {}

public func ==(lhs: NSOperatingSystemVersion, rhs: NSOperatingSystemVersion) -> Bool {
    return lhs.majorVersion == rhs.majorVersion && lhs.minorVersion == rhs.minorVersion
        && lhs.patchVersion == rhs.patchVersion
}

// Use like so:

if Configuration(idiom: .Pad, os: NSOperatingSystemVersion(majorVersion: 8, minorVersion: 3, patchVersion: 0)) {
    println("I'm an iPad running 8.3")
    // Do something useful
}

if Configuration(idiom: .Phone) {
    println("I'm any iPhone")
}

// OR: as function with a closure

func configuration(idiom: UIUserInterfaceIdiom? = nil, atLeast: NSOperatingSystemVersion? = nil, then: () -> Void) {
    var configuration = true
    if let idiom = idiom {
        configuration = idiom == UIDevice.currentDevice().userInterfaceIdiom
    }
    if let atLeast = atLeast {
        configuration = configuration && NSProcessInfo().isOperatingSystemAtLeastVersion(atLeast)
    }
    if configuration {
        then()
    }
}

// Usage:

configuration(idiom: .Phone, atLeast: NSOperatingSystemVersion(majorVersion: 8, minorVersion: 0, patchVersion: 0)) {
    println("I'm a phone running at least iOS8")
}