An extension providing runtime value extraction and debug utilities for Swift types.

Mirror+Extraction.swift

//
//  Mirror+Extraction.swift
//
//  Created by Stephan Casas on 1/31/25.
//

import Foundation

extension Mirror {

  /// The first child of this subject whose label matches the given string.
  func firstChild<T>(matching label: String, as type: T.Type) -> T? {
    for child in children {
      if child.label == label {
        return child.value as? T
      }
    }

    for child in children {
      let childMirror = Mirror(reflecting: child.value)
      if let found = childMirror.firstChild(matching: label, as: T.self) {
        return found
      }
    }

    return nil
  }

  /// The first child of the given subject whose label matches the given string.
  static func firstChild<T>(
    matching label: String, in subject: Any, as type: T.Type
  ) -> T? {
    Mirror(reflecting: subject).firstChild(matching: label, as: T.self)
  }

  /// Crawl the given subject's internal reflection tree — printing each child's label and value.
  static func debugPrint(_ subject: Any) {
    Self._debugPrint(subject)
  }

  private static func _debugPrint(_ subject: Any, indent: String = "") {
    let mirror = Mirror(reflecting: subject)

    if mirror.children.isEmpty {
      return
    }

    for child in mirror.children {
      if let label = child.label {
        print("\(indent)\(label): \(child.value)")
      } else {
        print("\(indent)\(child.value)")
      }

      Mirror._debugPrint(child.value, indent: indent + "  ")
    }
  }

}