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What language are you using? I'm using C# at work, but dabble in F# in my free time. I try to find a F# alternative to the C# way, seems like the simplest alter

by peheje 3y ago

What language are you using? I'm using C# at work, but dabble in F# in my free time. I try to find a F# alternative to the C# way, seems like the simplest alternative to dependency injection through containers are just function passing in F#, like you are mentioning. One thing that I would like to know, is how do you do the equivalent of "registering dependencies" like you would using a DI-container. Where do you setup all the (partially applied) "real" functions and all the "fake/mock" functions etc. I guess it's just a matter of structuring it in a nice way.

pharmakom 3y ago
If using F# the easiest way is usually to make an interface for the impure stuff and write a mock implementation of that. Pass the interface in as a parameter to your functions. Keep that interface as small as possible.
asimpletune 3y ago
The above related mostly to work I did in Scala, but I am writing mostly Rust now. Each language has a way of doing things so you have to adapt what I said to how it makes sense for you. Still, the process is the same in spirit. > how do you do the equivalent of “registering dependencies” In what I was describing earlier, dependency injection is literally just calling a function. The dependencies are arguments to a function, and you “inject” them by supplying them to the function. The “registering” is just based on your function signature. That is already a contract. Dependencies are functions too. > where do ou setup all the functions Usually one of two places: tests or your app’s entry point. In tests you just setup your function wherever it’s needed. Like I said if you need to test what happens when a dependency of yours does something, then just write a function that returns what you are looking to test. For your app, this same thing is in your app’s entry point, like main. So you read from config and build your dependencies, and then at the end you ultimately pass them to a function. At the end of the day this is about inversion of control, but it’s something that makes more sense if you invent it on your own from scratch before trying to understand what that means through more complicated abstractions.

by peheje 3y ago

pharmakom 3y ago

If using F# the easiest way is usually to make an interface for the impure stuff and write a mock implementation of that. Pass the interface in as a parameter to your functions. Keep that interface as small as possible.

asimpletune 3y ago

The above related mostly to work I did in Scala, but I am writing mostly Rust now. Each language has a way of doing things so you have to adapt what I said to how it makes sense for you. Still, the process is the same in spirit. > how do you do the equivalent of “registering dependencies” In what I was describing earlier, dependency injection is literally just calling a function. The dependencies are arguments to a function, and you “inject” them by supplying them to the function. The “registering” is just based on your function signature. That is already a contract. Dependencies are functions too. > where do ou setup all the functions Usually one of two places: tests or your app’s entry point. In tests you just setup your function wherever it’s needed. Like I said if you need to test what happens when a dependency of yours does something, then just write a function that returns what you are looking to test. For your app, this same thing is in your app’s entry point, like main. So you read from config and build your dependencies, and then at the end you ultimately pass them to a function. At the end of the day this is about inversion of control, but it’s something that makes more sense if you invent it on your own from scratch before trying to understand what that means through more complicated abstractions.