Loop through Swift struct to get keys and values - swift

Question

I'd like to loop trough every key of mystruct and print its key and its value for every property.
struct mystruct {
var a = "11215"
var b = "21212"
var c = "39932"
}
func loopthrough {
for (key, value) in mystruct {
print("key: \(key), value: \(value)") // Type mystruct.Type does not conform to protocol 'Sequence'
}
}
But using the few lines from above I always get this error message:
Type mystruct.Type does not conform to protocol 'Sequence'
How can I avoid getting this message?

Answer 1

First of all let's use CamelCase for the struct name
struct MyStruct {
var a = "11215"
var b = "21212"
var c = "39932"
}
Next we need to create a value of type MyStruct
let elm = MyStruct()
Now we can build a Mirror value based on the elm value.
let mirror = Mirror(reflecting: elm)
The Mirror value does allow us to access all the properties of elm, here's how
for child in mirror.children {
print("key: \(child.label), value: \(child.value)")
}
Result:
key: Optional("a"), value: 11215
key: Optional("b"), value: 21212
key: Optional("c"), value: 39932

Answer 2

use following code to get array of all the properties
protocol PropertyLoopable
{
func allProperties() throws -> [String]
}
extension PropertyLoopable {
func allProperties() throws -> [String] {
var result: [String] = []
let mirror = Mirror(reflecting: self)
// Optional check to make sure we're iterating over a struct or class
guard let style = mirror.displayStyle, style == .struct || style == .class else {
throw NSError()
}
for (property,_) in mirror.children {
guard let property = property else {
continue
}
result.append(property)
// result[property] = value
}
return result
}
}
Now just
let allKeys = try self.allProperties()
Don't forgot to implement protocol
Hope it is helpful

Answer 3

You can use runtime introspection (on an instance of your type) combined with value-binding pattern matching to extract the property names and values; the latter used to unwrap the optional label property of the Mirror instance used to represent the sub-structure of your specific instance.
E.g.:
struct MyStruct {
let a = "11215"
let b = "21212"
let c = "39932"
}
// Runtime introspection on an _instance_ of MyStruct
let m = MyStruct()
for case let (label?, value) in Mirror(reflecting: m)
.children.map({ ($0.label, $0.value) }) {
print("label: \(label), value: \(value)")
} /* label: a, value: 11215
label: b, value: 21212
label: c, value: 39932 */

Answer 4

I hope it still helps someone:
This is my version of the protocol for more complicated classes/structs (Objects within Objects within Objects ;-) )
I am sure there is a more elegant functional solution but this was a quick and dirty solution, as I only needed it for a temporary log.
protocol PropertyLoopable {
func allProperties() -> [String: Any]
}
extension PropertyLoopable {
func allProperties() -> [String: Any] {
var result: [String: Any] = [:]
let mirror = Mirror(reflecting: self)
// make sure we're iterating over a struct or class
guard let style = mirror.displayStyle, style == .struct || style == .class else {
print("ERROR: NOT A CLASS OR STRUCT")
return result
}
for (property, value) in mirror.children {
guard let property = property else {
continue
}
// It was a very complicated struct from a JSON with a 4 level deep structure. This is dirty dancing, remove unnecessary "for" loops for simpler structs/classes
// if value from property is not directly a String, we need to keep iterating one level deeper
if value is String {
result.updateValue(value, forKey: property)
} else {
let mirror = Mirror(reflecting: value)
for (property, value) in mirror.children {
guard let property = property else {
continue
}
//let's go for a second level
if value is String {
result.updateValue(value, forKey: property)
} else {
let mirror = Mirror(reflecting: value)
for (property, value) in mirror.children {
guard let property = property else {
continue
}
//3rd level
if value is String {
result.updateValue(value, forKey: property)
} else {
let mirror = Mirror(reflecting: value)
for (property, value) in mirror.children {
guard let property = property else {
continue
}
result.updateValue(value, forKey: property)
}
}
}
}
}
}
}
return result
}
}