java - 斯卡拉中的 "built in dependency injection"

Question

你好下面的帖子说scala中有“内置依赖注入(inject)”

"As a Scala and Java developer, I am not even slightly tempted to replace Scala as my main language for my next project with Java 8. If I'm forced to write Java, it might better be Java 8, but if I have a choice, there are so many things (as the OP correctly states) that make Scala compelling for me beyond Lambdas that just adding that feature to Java doesn't really mean anything to me. Ruby has Lambdas, so does Python and JavaScript, Dart and I'm sure any other modern language. I like Scala because of so many other things other than lambdas that a single comment is not enough.

But to name a few (some were referenced by the OP)

Everything is an expression, For comprehensions (especially with multiple futures, resolving the callback triangle of death in a beautiful syntax IMHO), Implicit conversions, Case classes, Pattern Matching, Tuples, The fact that everything has equals and hashcode already correctly implemented (so I can put a tuple, or even an Array as a key in a map), string interpolation, multiline string, default parameters, named parameters, built in dependency injection, most complex yet most powerful type system in any language I know of, type inference (not as good as Haskell, but better than the non existent in Java). The fact I always get the right type returned from a set of "monadic" actions thanks to infamous things like CanBuildFrom (which are pure genius). Let's not forget pass by name arguments and the ability to construct a DSL. Extractors (via pattern matching). And many more.

I think Scala is here to stay, at least for Scala developers, I am 100% sure you will not find a single Scala developer that will say: "Java 8 got lambdas? great, goodbye scala forever!". Only reason I can think of is compile time and binary compatibility. If we ignore those two, all I can say is that this just proves how Scala is in the right direction (since Java 8 lambdas and default interface methods and steams are so clearly influenced)

I do wish however that Scala will improve Java 8 interoperability, e.g. support functional interfaces the same way. and add new implicit conversions to Java 8 collections as well as take advantage to improvements in the JVM.

I will replace Scala as soon as I find a language that gives me what Scala does and does it better. So far I didn't find such a language (examined Haskell, Clojure, Go, Kotlin, Ceylon, Dart, TypeScript, Rust, Julia, D and Nimrod, Ruby Python, JavaScript and C#, some of them were very promising but since I need a JVM language, and preferably a statically typed one, it narrowed down the choices pretty quickly)

Java 8 is by far not even close, sorry. Great improvement, I'm very happy for Java developers that will get "permission" to use it (might be easier to adopt than Scala in an enterprise) but this is not a reason for a Scala shop to consider moving back to Java." [1]

scala 中的内置依赖注入(inject)到底是什么？

Answer 1

这不是一个独立的语言功能。我认为作者指的是这样一个事实，即 Scala 的功能集足够灵活，可以支持许多可以说是完成 DI 的技术:

• > the cake pattern , 建立在特质系统上
• > the Reader monad , 建立在更高种类的类型上
• > DI through currying , 以功能技术为基础
• > using implicit class parameters ，建立在 Scala 的隐式概念之上
• 在我自己的项目中，我们通过显式要求类构造函数中的函数值来完成 DI

这种多样性是 Scala 的象征。该语言旨在实现许多非常强大的概念，大部分是正交的，从而产生多种有效的方法来解决许多问题。作为 Scala 程序员的挑战是理解这个广度，然后为您的项目做出明智的选择。很多时候，该选择取决于内部使用哪些范例来实现您的组件。