Setup package

.github/workflows/ci.yml

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+name: CI
+on: [push, pull_request]
+
+jobs:
+  test:
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest]
+    runs-on: ${{matrix.os}}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Tests
+        run: swift test --enable-code-coverage
+      - name: codecov
+        run: |
+          os=$(echo "${{ matrix.os }}" | cut -f1 -d"-")
+
+          if [ "$os" = "ubuntu" ]; then
+            sudo ln -s /usr/lib/llvm-9/bin/llvm-cov /usr/local/bin/llvm-cov
+            object=".build/debug/ComposePackageTests.xctest"
+          elif [ "$os" = "macos" ]; then
+            sudo ln -s /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/llvm-cov /usr/local/bin/llvm-cov
+            object=".build/debug/ComposePackageTests.xctest/Contents/MacOS/ComposePackageTests"    
+          fi
+
+          llvm-cov export -format="lcov" --object "$object" -instr-profile .build/debug/codecov/default.profdata > info.lcov
+          bash <(curl https://codecov.io/bash) -cF "$os"

.gitignore

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+
+# Created by https://www.gitignore.io/api/xcode,macos,swift,swiftpm,swiftpackagemanager
+# Edit at https://www.gitignore.io/?templates=xcode,macos,swift,swiftpm,swiftpackagemanager
+
+### macOS ###
+# General
+.DS_Store
+.AppleDouble
+.LSOverride
+
+# Icon must end with two \r
+Icon
+
+# Thumbnails
+._*
+
+# Files that might appear in the root of a volume
+.DocumentRevisions-V100
+.fseventsd
+.Spotlight-V100
+.TemporaryItems
+.Trashes
+.VolumeIcon.icns
+.com.apple.timemachine.donotpresent
+
+# Directories potentially created on remote AFP share
+.AppleDB
+.AppleDesktop
+Network Trash Folder
+Temporary Items
+.apdisk
+
+### Swift ###
+# Xcode
+#
+# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
+
+## Build generated
+build/
+DerivedData/
+
+## Various settings
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata/
+
+## Other
+*.moved-aside
+*.xccheckout
+*.xcscmblueprint
+
+## Obj-C/Swift specific
+*.hmap
+*.ipa
+*.dSYM.zip
+*.dSYM
+
+## Playgrounds
+timeline.xctimeline
+playground.xcworkspace
+
+# Swift Package Manager
+# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
+# Packages/
+# Package.pins
+# Package.resolved
+.build/
+# Add this line if you want to avoid checking in Xcode SPM integration.
+.swiftpm/xcode
+
+# CocoaPods
+# We recommend against adding the Pods directory to your .gitignore. However
+# you should judge for yourself, the pros and cons are mentioned at:
+# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
+# Pods/
+# Add this line if you want to avoid checking in source code from the Xcode workspace
+# *.xcworkspace
+
+# Carthage
+# Add this line if you want to avoid checking in source code from Carthage dependencies.
+# Carthage/Checkouts
+
+Carthage/Build
+
+# Accio dependency management
+Dependencies/
+.accio/
+
+# fastlane
+# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
+# screenshots whenever they are needed.
+# For more information about the recommended setup visit:
+# https://docs.fastlane.tools/best-practices/source-control/#source-control
+
+fastlane/report.xml
+fastlane/Preview.html
+fastlane/screenshots/**/*.png
+fastlane/test_output
+
+# Code Injection
+# After new code Injection tools there's a generated folder /iOSInjectionProject
+# https://github.com/johnno1962/injectionforxcode
+
+iOSInjectionProject/
+
+### SwiftPackageManager ###
+Packages
+xcuserdata
+*.xcodeproj
+
+
+### SwiftPM ###
+
+
+### Xcode ###
+# Xcode
+# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
+
+## User settings
+
+## compatibility with Xcode 8 and earlier (ignoring not required starting Xcode 9)
+
+## compatibility with Xcode 3 and earlier (ignoring not required starting Xcode 4)
+
+## Xcode Patch
+*.xcodeproj/*
+!*.xcodeproj/project.pbxproj
+!*.xcodeproj/xcshareddata/
+!*.xcworkspace/contents.xcworkspacedata
+/*.gcno
+
+### Xcode Patch ###
+**/xcshareddata/WorkspaceSettings.xcsettings
+
+# End of https://www.gitignore.io/api/xcode,macos,swift,swiftpm,swiftpackagemanager

LICENSE

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+MIT License
+
+Copyright (c) 2020 Andrés Cecilia Luque
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

Package.swift

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+// swift-tools-version:5.0
+
+import PackageDescription
+
+let package = Package(
+    name: "Compose",
+    products: [
+        .library(name: "Compose", targets: ["Compose"]),
+    ],
+    dependencies: [],
+    targets: [
+        .target(
+            name: "Compose",
+            dependencies: []
+        ),
+        .testTarget(
+            name: "ComposeTests",
+            dependencies: ["Compose"]
+        ),
+    ]
+)

README.md

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+# Compose
+
+[![CI](https://github.com/acecilia/Compose/workflows/CI/badge.svg?branch=master)](https://github.com/acecilia/Compose/actions)
+[![CI](https://codecov.io/gh/acecilia/Compose/branch/master/graph/badge.svg)](https://codecov.io/github/acecilia/Compose)
+
+## What is this?
+
+A Swift library for composing structs from other structs, which relies on the `KeyPath` and `@dynamicMemberLookup` features to provide a clean and typesafe API:
+
+```swift
+import Compose
+
+struct Developer: Codable, Hashable {
+    var name: String
+    var age: Int
+}
+
+struct RemoteLocation: Codable, Hashable {
+    var country: String
+    var city: String
+}
+
+typealias RemoteDeveloper = Compose<Developer, RemoteLocation>
+
+let remoteDeveloper = RemoteDeveloper(
+    .init(name: "Andres", age: 26), 
+    .init(country: "Spain", city: "Madrid")
+)
+print(remoteDeveloper.name) // Andres
+print(remoteDeveloper.city) // Madrid
+```
+
+For an in depth explanation please [follow this link](https://www.sforswift.com/posts/composition-using-keypath-and-dynamic-member-lookup/).
+
+## Installation
+
+### Swift Package Manager
+
+Add the following to the dependencies inside your `Package.swift` file:
+
+```swift
+.package(url: "https://github.com/acecilia/Compose.git", .upToNextMajor(from: "0.0.1")),
+```
+
+## License
+
+Compose is licensed under the MIT license. See [LICENSE](LICENSE) for more info.

Sources/Compose/Compose.swift

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+import Foundation
+
+@dynamicMemberLookup
+public struct Compose<Element1, Element2> {
+    public var element1: Element1
+    public var element2: Element2
+
+    public subscript<T>(dynamicMember keyPath: WritableKeyPath<Element1, T>) -> T {
+        get { element1[keyPath: keyPath] }
+        set { element1[keyPath: keyPath] = newValue }
+    }
+
+    public subscript<T>(dynamicMember keyPath: WritableKeyPath<Element2, T>) -> T {
+        get { element2[keyPath: keyPath] }
+        set { element2[keyPath: keyPath] = newValue }
+    }
+
+    public init(_ element1: Element1, _ element2: Element2) {
+        self.element1 = element1
+        self.element2 = element2
+    }
+}
+
+// MARK - Conformances
+
+extension Compose: Encodable where Element1: Encodable, Element2: Encodable {
+    public func encode(to encoder: Encoder) throws {
+        try element1.encode(to: encoder)
+        try element2.encode(to: encoder)
+    }
+}
+
+extension Compose: Decodable where Element1: Decodable, Element2: Decodable {
+    public init(from decoder: Decoder) throws {
+        self.element1 = try Element1(from: decoder)
+        self.element2 = try Element2(from: decoder)
+    }
+}
+
+extension Compose: Equatable where Element1: Equatable, Element2: Equatable { }
+
+extension Compose: Hashable where Element1: Hashable, Element2: Hashable { }
+
+extension Compose: Error where Element1: Error, Element2: Error { }
+
+extension Compose: LocalizedError where Element1: LocalizedError, Element2: LocalizedError {
+    public var errorDescription: String? {
+        [element1.errorDescription, element2.errorDescription].filterAndJoin()
+    }
+    public var failureReason: String? {
+        [element1.failureReason, element2.failureReason].filterAndJoin()
+    }
+    public var recoverySuggestion: String? {
+        [element1.recoverySuggestion, element2.recoverySuggestion].filterAndJoin()
+    }
+    public var helpAnchor: String? {
+        [element1.helpAnchor, element2.helpAnchor].filterAndJoin()
+    }
+}
+
+private extension Array where Element == String? {
+    func filterAndJoin() -> String {
+        return compactMap { $0 }.joined(separator: "\n")
+    }
+}
+
+// MARK - typealiases for composition with multiple types
+
+public typealias Compose3<T1, T2, T3> =
+    Compose<T1, Compose<T2, T3>>
+
+public typealias Compose4<T1, T2, T3, T4> =
+    Compose<Compose<T1, T2>, Compose<T3, T4>>
+
+public typealias Compose5<T1, T2, T3, T4, T5> =
+    Compose<Compose<T1, T2>, Compose<T3, Compose<T4, T5>>>

Tests/ComposeTests/ComposeMultipleTests.swift

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+import XCTest
+import Foundation
+import Compose
+
+final class ComposeMultipleTests: XCTestCase {
+    func testGetSet() {
+        let expectedName = "Kike"
+        let expectedCity = "Segovia"
+        let expectedTeam = "Android"
+
+        var mutable = remoteTeamLead
+        mutable.name = expectedName
+        mutable.city = expectedCity
+        mutable.team = expectedTeam
+
+        XCTAssertEqual(mutable.name, expectedName)
+        XCTAssertEqual(mutable.city, expectedCity)
+        XCTAssertEqual(mutable.team, expectedTeam)
+    }
+
+    func testCodable() throws {
+        guard #available(OSX 10.13, *) else {
+            XCTFail()
+            return
+        }
+
+        let remoteTeamLeadJson = """
+        {
+          "age" : 26,
+          "city" : "Madrid",
+          "country" : "Spain",
+          "name" : "Andres",
+          "salary" : 1000000,
+          "team" : "iOS"
+        }
+        """
+
+        let decoder = JSONDecoder()
+        let remoteDeveloper = try decoder.decode(RemoteTeamLead.self, from: Data(remoteTeamLeadJson.utf8))
+
+        let encoder = JSONEncoder()
+        encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
+        let data = try encoder.encode(remoteDeveloper)
+
+        XCTAssertEqual(remoteTeamLeadJson, String(data: data, encoding: .utf8))
+    }
+}