Revisit Dependency Injection in scala

Revisit Dependency Injection in scala

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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Revisit Dependency Injection in Scala Naoki Takezoe @takezoen at Airframe Meetup #3
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. What’s Dependency Injection? ● Inversion of Control ● Externalize components dependency and make it configurable ● Encourage clean components design ● Components can be replaced (e.g. for testing) ● Good collaboration with Aspect Oriented Programming
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Dependency Injection in Java Explicit configuration to Less configuration
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Dependency Injection in Scala ● Java based DI container ○ Google Guice ● Pure Scala approach ○ Implicit parameter ○ Cake Pattern ○ Reader Monad, etc ● Scala native DI library ○ MacWire ○ Airframe
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Google Guice ● Widely used in Scala because of Play Framework ● Easy to use and understand ● Lack of Scala specific functionality Define binding in Module Use @Inject annotation for DI
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Implicit parameter ● No external library is required ● Easy to use and understand ● All necessary components must be in the same scope Take necessary components as implicit parameter Define necessary implicit val or def in the execution scope
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Cake Pattern ● No external library is required ● Boilerplate Combine by mix-in Declare dependency as self-type annotation
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Reader Monad ● Carry components around as an environment ● Need to put all necessary components together into the environment Run with environment
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. MacWire ● Generate instance creation code with constructor injection by macro ● Rich features (e.g. multi binding, tagged binding, intercepter, etc) ● No boilerplate ● All necessary components must be in the same scope Create instance using wire[T] macro
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Airframe ● Constructor injection and In-trait injection ● Rich features (e.g. tagged binding, type alias binding, config binding, etc) ● Less configuration by automatic instance creation ● Life-cycle management In-trait injection Define binding on Design if you need to override default binding
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Runtime DI vs Compile-time DI ● Runtime DI ○ Google Guice ○ Airframe ● Compile-time ID ○ Pure Scala approaches ○ MacWire
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. Runtime DI vs Compile-time DI Runtime DI Compile-time DI Binding error Runtime error Compilation error Configuration Less configuration Boilerplate is necessary Life-cycle management Yes No Overhead Runtime Compile-time External library Required Not required / Required Scala specific features Yes / No Yes
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  Copyright 1995-2019 ArmLimited (or its affiliates). All rights reserved. What approach is the best? ● Do you need auto-wiring? ● Which do you need? compile-time dependency check or dynamic-type binding? ● Do you need object life-cycle management?
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  Thank You! Danke! Merci! 谢谢! ありがとう! Gracias! Kiitos! Copyright 1995-2019Arm Limited (or its affiliates). All rights reserved.