enum EnumType {
case WithString(String)
}
var enums = [EnumType]()
enums.append(EnumType.WithString("A"))
enums.append(EnumType.WithString("B"))
enums.append(EnumType.WithString("C"))
enums.append(EnumType.WithString("D"))
enums.append(EnumType.WithString("E"))
enums.append(EnumType.WithString("F"))
How to filter my enums array to find the one with associated value equal C. What predicate do I need to use?
The filter function can either be invoked as a global function over an array, or as an instance method (I prefer the later as it is more OO).
It accepts a closure with one parameter (the element being evaluated) that return a boolean (indicating whether the element matches the required condition).
Since it's a simple closure in a clear situation it's ok to use the abbreviated form.
I guess that other "With" cases would be added to your enum, so you could go with something like:
let filteredArray = enums.filter {
switch $0 {
case .withString(let value):
return value == "C"
default:
return false
}
}
That should do the trick in your example.
rawValue.As someone already mentioned, for Swift > 2.0 there's if case statement available:
enums.filter {
if case .WithString("C") = $0 {
return true
}
return false
}
But, it doesn't look nice, especially if you are going to repeat same logic again. What we can do here is to make EnumType conform to Equatable:
extension EnumType: Equatable {
}
func ==(lhs: EnumType, rhs: EnumType) -> Bool {
switch (lhs, rhs) {
case (.WithString(let lStr), .WithString(let rStr)):
return lStr == rStr
}
}
And now you can just:
enums.filter { $0 == .WithString("C") }
You could try adding a simple extension with a computed property to your enum and filter to that property:
extension EnumType {
var isC: Bool {
switch self {
case .WithString(let message): return message == "C"
default: return false
}
}
}
After this, you could simpy use the filtering as usual:
enums.filter { $0.isC }
var filteredArray = enums.filter { element in
switch element {
case EnumType.WithString(let string):
return string == "A"
default:
return false
}
}
This can probably be simplified with Swift 2.0 binding of assosciated values in if statements.
Inspired by @Jessy and SwiftLee, here is my solution:
// -----------------------
// CaseReflectable
// -----------------------
// designed for enums only
// (use it on other types not recommended)
protocol CaseReflectable {}
// default behaviors.
extension CaseReflectable {
/// case name
var caseName: String {
let mirror = Mirror(reflecting: self)
// enum cases:
// - normal case: no children
// - case with associated values: one child (with label)
guard let label = mirror.children.first?.label else {
return "\(self)" // normal case
}
// case with associated values
return label
}
/// associated values
var associatedValues: Any? {
// if no children, a normal case, no associated values.
guard let firstChild = Mirror(reflecting: self).children.first else {
return nil
}
return firstChild.value
}
}
// --------------------------
// custom operator ~=
// --------------------------
/// match enum cases with associated values, while disregarding the values themselves.
/// usage: `Enum.enumCase ~= instance`
func ~= <Enum: CaseReflectable, AssociatedValue>(
// an enum case (with associated values)
enumCase: (AssociatedValue) -> Enum, // enum case as function
// an instance of Enum
instance: Enum
) -> Bool
{
// if no associated values, `instance` can't be of `enumCase`
guard let values = instance.associatedValues else { return false }
// if associated values not of the same type, return false
guard values is AssociatedValue else { return false }
// create an instance from `enumCase` (as function)
let case2 = enumCase(values as! AssociatedValue)
// if same case name, return true
return case2.caseName == instance.caseName
}
// ------------
// Enum
// ------------
// enum with associated values
// (conforms to `CaseReflectable`)
enum Enum: CaseReflectable {
case int(Int)
case int2(Int)
case person(name: String, age: Int)
case str(String)
}
// ------------
// main
// ------------
let a: Enum = .int(3)
Enum.int ~= a // true
Enum.int2 ~= a // false
let joe = Enum.person(name: "joe", age: 8)
Enum.person ~= joe // true
Enum.int ~= joe // false
// array of enum cases
let items: [Enum] = [
.int(1), .str("hi"), .int(2)
]
// filter enum cases
let filtered = items.filter { Enum.int ~= $0 }
print(filtered) // [Enum.int(1), Enum.int(2)]
You can achieve something more reusable by implementing Equatable protocol:
enum EnumType {
case WithString(String)
}
extension EnumType: Equatable {
static func ==(lhs: EnumType, rhs: String) -> Bool {
switch lhs {
case .WithString(let value):
return value == rhs
}
}
}
EnumType.WithString("F") == "A" // false
EnumType.WithString("F") == "F" // true
