Slide 1
Slide 1 text
Dependency
Injection in Swift
Potatotips-27, March 16, 2016
@yoichitgy - Yoichi Tagaya
Slide 2
Slide 2 text
DI Container for Swift
https://github.com/Swinject/Swinject
Swinject
Slide 3
Slide 3 text
try! Swift Conference Day 3
http://niwatako.hatenablog.jp/entry/2016/03/04/182144
http://niwatako.hatenablog.jp/entry/2016/03/04/130940
Veronica Ray
Ash Furrow
Good to use DI
Why Use Dependency Injection (DI)
- Easy customization
- Clear ownership
- Testability
http://www.tryswiftconf.com
“
“
Slide 4
Slide 4 text
Dependency Injection is...
https://en.wikipedia.org/wiki/Dependency_injection
Pattern implementing inversion of control
for resolving dependencies.
Wikipedia:
Slide 5
Slide 5 text
Inversion of Control
• I'm talking to you.
/ You're talking to me.
• You call libraries.
/ Frameworks call you.
• You create what you use.
/ What you use are created (and passed).
Slide 6
Slide 6 text
Problem of Dependency Injection
/FUXPSL
$MBTT"
Dependency
Beginning...
let a = A(network: Network())
Dependency Injection
Slide 7
Slide 7 text
Problem of Dependency Injection
/FUXPSL
$MBTT"
4FOTPS
-PDBUJPO
4USVDU#
$MBTT$
Dependency
Soon later...
Slide 8
Slide 8 text
Problem of Dependency Injection
Much later...
/FUXPSL
$MBTT"
4FOTPS
-PDBUJPO
4USVDU#
$MBTT$
Dependency
4USVDU&
$MBTT%
$MBTT'
$MBTT(
$MBTT)
$MBTT*
Hard to manage
Slide 9
Slide 9 text
Solution: DI Container
Dependency graph
%*$POUBJOFS
Register the graph
Resolve when you need
*OTUBODFPG
$MBTT(
/FUXPSL
$MBTT"
4FOTPS
-PDBUJPO
4USVDU#
$MBTT$
4USVDU&
$MBTT%
$MBTT'
$MBTT(
$MBTT)
$MBTT*
Slide 10
Slide 10 text
Usage of Swinject - DI Container
protocol XType {
}
struct X: XType {
}
protocol YType {
}
class Y: YType {
let x: XType
init(x: XType) {
self.x = x
}
}
protocol ZType {
}
class Z: ZType {
let y: YType
init(y: YType) {
self.y = y
}
}
import Swinject
let container = Container()
container.register(XType.self) { _ in
X()
}
container.register(YType.self) { r in
Y(x: r.resolve(XType.self)!)
}
container.register(ZType.self) { r in
Z(y: r.resolve(YType.self)!)
}
Registration:
Resolution:
let z = container.resolve(ZType)!
Type definition:
Y→X
Z→Y
X
Automatically resolved: Z→Y→X
X
Y
Z
Slide 11
Slide 11 text
Summary
• Dependency Injection is good for mocking
and testing.
• DI container is useful for dependency
management.
• Swinject is a DI container framework for Swift.
Slide 12
Slide 12 text
Further Readings
• Dependency Injection Framework for Swift - Swinjectͷհ
http://qiita.com/yoichitgy/items/ed8aac4d6f1e6666a4aa
• Dependency Injection in Swift (Tokyo iOS Meetup)
https://speakerdeck.com/yoichitgy/dependency-injection-in-swift
• Unit Testing in Swift: Dependency Injection
https://www.natashatherobot.com/unit-testing-swift-dependency-injection/
• DI in Scala: Cake Pattern pros & cons
http://www.warski.org/blog/2011/04/di-in-scala-cake-pattern-pros-cons/
• You Used To Inject Me In Your Constructor (Reader Monad)
https://speakerdeck.com/mathonsunday/you-used-to-inject-me-in-your-constructor