Then it's just a massive waste of time and gets in the way.

I really feel that you (and Microsoft) have completely lost sight of the reason why DI was ever even necessary and have become blind to just how much extra code it generates. The only reason was to inject mocks, and people hand-wrung for ages over it because the code to do so infects all the other code. Then people started to try and back justify it with IoC, but it's never really been a convincing argument.

It's also something that if you're not working regularly with it can be very mysterious and when it fails, fails at run-time, quite inscrutably sometimes.

From my perspective it's just boilerplate magic that if you actually need it, fair enough, but if you don't is a persistent, nagging, pain in the ass.

In C# the idiomatic way to achieve this is via constructor injection, which is made much easier to manage in ASP.Net with a DI library that works with the framework for you (either the built in one or AutoFac / SimpleInjector, etc.). But you don't have to use a library; many times I'm writing a simple-ish console app and just use good old "Poor Man's DI" where I manually construct my object graphs at startup.

DIP is achieved precisely when the components (be they packages, projects, classes, types) are organized with the low-level modules depending on the high-level modules rather than vice versa. In English, this usually means the I/O and any heavy framework code is kept out of the program logic.

What DI does do is confuse this matter. Class relationships which are mere IMPLEMENTATION DETAILS of a module are elevated alongside the actual component architecture of the program. The object graph becomes obscured. Program execution order becomes nondeterministic. The callstack is completely ruined, undoing decades of enlightenment since Dijkstra's "GOTO statement considered harmful." And all my experience with the pattern proves, the DI container causes programmers to not even evaluate or understand whether their dependencies are even inverted, because all classes and their relationships just become one amorphous blob floating aimlessly inside the container.

Simply, this means that no implementation module, high or low, depends on any other implementation module, ever. It only ever depends on abstractions which are shared between modules.

I don't see how using a DI container can change the program execution order, unless one is misusing it terribly - after all, its sole purpose is to provide the correct concrete implementation of a dependency to an object at the time of its construction, the execution order from the perspective of the program is 100% preserved. Sure, maybe the container itself creates my graph in a non-deterministic way, but why would I care? If my program depends on this that's just bad design imo, no amount of libraries is going to save it :)

And the object graph is not obscured, in fact it is clarified, because you look at a class constructor and immediately can see what it's invariants are! And I have yet to come across a DI library that wouldn't immediately halt and catch fire if you introduced a circular dependency chain, so it's literally not possible to have these amorphous blobs (great expression though!) in any proper DI container.

+1. This simple idea is the basis of Clean Code, Hexagonal Architecture, Onion Architecture, Haskell, Functional-Core-Imperative-Shell, among other good architecture ideas.

If you're not using abstractions, you are not using the DIP. What is being described here with low-level modules depending on high-level modules is categorically not the DIP, and I am starting to wonder if this is perhaps part of the frustration that the poster we're replying to has experienced with DI, since turning your coupling upside down will have the same problems as just high coupling in general, except everything is upside down now and harder to read :)

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I agree with your take on DIP.

We're using Microsoft Service Collection and with the Scrutor nuget component we were able to easily decorate an implementation from another package to extend the functionality adhering to the open closed principle OCP.

DI also enables your code to be open for extension but closed for modification.

Great stuff!

I like C#, no, I adore C#. I have a bad memory for even the simplest method calls and the sheer power the intellisense in a statically typed language gives me to just not care means I can just code with joy.

My personal view on it has always been that someone in MS wrote MVC 1 in response to Rails on the sly. It was fantastic, a breath of fresh air into the MS constant misunderstanding of the web. Especially compared to webforms. For a while, everything was good. Then somehow 7 or 8 years ago the ASP.Net team got obsessed with ramming "best practices" down our throat and everything's gone a bit downhill from there.

And they don't even have a point in this regard, because nothing is forcing you to use the DI. You wanna make a database connection with ADO.NET and a static connection string in your Controller? Go ahead. You can do that. It's no more effort than it ever was.

You want to grow your app to run it in multiple environments and be confident you don't clobber your configuration during migrations? Use ASP.NET Core's DI.

Every app framework has some "magic convention over configuration". I personally think ASP.NET Core's "magic" is a lot less pervasive than in, say Django, or RoR. When I was first learning ASP.NET Core--coming from WebForms--there was a learning curve. You don't just throw everything into a Web.config XML bag of doom anymore, with a single, static configuration reading tool that reads just that one file. That particular magic has changed. I mean, if you want to do that, you can, just read the file yourself. But it's not wired up by default anymore. And the new way of doing things was easily learned with a couple of afternoons of reading the documentation.

Which you can do, because there is actually documentation, and a lot of it. I think part of the problem might be that people are used to other web app frameworks where the documentation is pretty lacking, so they don't even think to go looking for documentation on ASP.NET Core and think they can just jump in and figure it out. I don't think you could do that going from Django to RoR or vice versa, but people complain when they can't go from ASP.NET WebForms to ASP.NET Core without learning new ways of doing things.

Don't like ASP.NET Core? You don't even have to use it. You can (rather easily) write your own web app framework. I've done it in the past, and there are FOSS projects for doing it (https://suave.io/, https://www.abp.io/, https://giraffe.wiki/, https://dotnetify.net/, https://www.dotvvm.com/, https://coalesce.intellitect.com/).

1) that graph of object creation is NOT equal to graph of object usage

2) if you don't use DI, problems won't automagically go away - code will _still_ have dependencies, just they'll be hidden and tightly coupled

It is precisely when you use a DI container that the problem is hidden, whether or not it's solved.

In most projects that use a DI container, the problem is usually not solved correctly, but the developers are oblivious and overconfident. They think, as you do, using a DI container means they did it right. False! The DI container only guarantees everything is hoisted up to the object constructor. This is NOT DEPENDENCY INVERSION. The objects can be in the constructor, but the dependency arrow can still point the wrong way. An obvious example of this I've seen a million times is an interface sitting right next to its only implementation. That's NOT Dependency Inversion.

If you don't use a DI container, the problem also may or may not be solved, but it is never obscured, it is completely visible.

Also, one can use DI without DI containers. Actually I prefer not using DI containers when possible.

Write a util function then, or like some like to call it, one of the many Factory pattern.

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https://web.archive.org/web/20200502175326/http://misko.heve...

#1 Because the language provides no means to arbitrarily mock fields of a class, an entire design pattern and framework needs to be created just to do so. Why can't the language just have such a feature?

#2 This actually temps people in building worse design, because instead of creating pure units that don't have dependencies to begin with, it facilitates the opposite of creating deeply nested chains of dependencies, because "DI framework wires it up for me". Where if you didn't have that luxury, you'd be pushed towards pure units that don't have state dependencies, and integ tests instead, which in my mind is much better overall.

#2 What stops you from creating a complex system without having dependencies, thus avoiding DI? Also, I think it would make an interesting case study if you're willing to write it.

I don't think I did. Someone says, well if you use new, how are you going to unit test your class?

And one answer from a user of the language would be: Ya, I guess you'd need to change the way you're creating dependencies so they happen in the caller, and then you'd need to change your class so it takes the instance on its constructor, etc.

And this is the original OPs issue with C#, all the ceremony involved.

Another answer would be that the C# language designer could build a language level feature that avoids having to do that and allows mocking new inside a unit so it can be easily tested without shenanigans.

In fact, in Java-land, there is a library that lets you unit tests classes that use new, it's called Powermock. So it is feasible.

> #2 What stops you from creating a complex system without having dependencies, thus avoiding DI? Also, I think it would make an interesting case study if you're willing to write it.

I've moved to a functional language instead personally. That said, I do still like C# and Java, and think they are great languages. I'm also not against DI, or other enterprise patterns, some have legitimate uses. But I have definitely seen what the OP is complaining about, those languages are too deep in their own rabbit hole sometimes. To the point that half the developers don't know why they use DI, that's just part of the template they used to bootstrap their app. There's no thought process about, wait, what is the issue in my code structure and design that I'm facing, and what could I do to solve it. Instead it's just, I'm using all the "best practices", they are the best, and I'm using them all, all the time, so my code is the best it can be. Without any thought about what advantages they're even getting out of it.

That's why I asked about the "new". Most people don't really know the pros/cons. They only repeat what they read blindly: "New" bad bad, no use "new", never, very bad, antipattern, here link proof, must use DI instead.

And sometimes when they know of a cons, they don't think about tradeoffs against alternatives. They just say, well it has this one con, so it's very bad! An antipattern!

I think that creates a setting where you get monstrous framework and code bases, where people just throw every known pattern at it, no matter if it was called for or not.

> just they'll be hidden and tightly coupled

They're more hidden with DI than without, in my experience.

At any rate, having left the .NET stack around 5 years ago, I certainly don't miss DI. My current code has more and better tests than my C# code ever did, so DI didn't really help me there (nor did it hinder me-- it was neutral). But my current code is much more explicit, direct, and a fair bit more compact. I'm definitely happier with it.

To me, answer is clear - class A has obvious and loosely coupled ones. Lo and behold, class A comes from program which uses DI. Class B doesn't.

You can still depend on abstractions without DI. Just use an interface or asbtract class in your code.

DI only plays into how you acquire yourself an instance of the concrete class for that abstraction you depend on.

So it can be given to you by your caller (DI). You can go fetch it somewhere (ServiceLocator). You can create it through a utility (Factory). Or you can create it yourself old fashion way with new.

> But you don't have to use a library; many times I'm writing a simple-ish console app and just use good old "Poor Man's DI" where I manually construct my object graphs at startup

I will support that. I'd like people to be precise in their criticism, do you find the DI pattern troublesome, or some particular DI framework?

I was kind of making the same point as you did, that you don't need to use any kind of DI library to achieve the DIP, but that in something like ASP.Net it is there and simple to use.

I am not sure what is a better way to solve this problem, but the original OP is right - it's far too much ceremony.

I think it is ok to depend on a DI-container in your unit tests for dependencies you are not directly testing, instead of stubs or manually instantiating them, to avoid updating unrelated unit tests when some class changes it's dependency somewhere in your project.

Instead I prefer system/integration tests where you test lets say a complete request from start to finish. Now your code base can change as much as you like, dependencies can be added or removed or classes or packages can be completely deleted, the tests stays the same. And now you are having tests that much closer matches reality instead of tons of mocks and stubs that can easily fool you to believing that they represent a good estimate of reality.

By doing this way a constructor based DI does not become a nuisance instead it helps you to organize your project, as it should be. Using a DI container makes it natural to break down your classes and automatically share the same decencies between them.

Counterargument to my argument is that if you don't use constructor based DI you can rewrite your class in anyway you like and the test stays the same, that is all true, however what DI gives you is the possibility to change the behavior of a class from the outside by injecting different dependencies, this makes your code better structured and easier to reuse.

If you want to accomplish that in the non-DI case you have to go thru trouble of configurable proxy classes which just introduces one more layer of bureaucracy, the thing you wanted to avoid by not doing DI.

My own criticism of DI containers is that they introduce magic to the project, personally I truly dislike code magic, however a DI container is nothing more than on the fly factory creator. In theory you could remove the DI container from a project by manually writing factories for each execution path, for me that becomes an acceptable level of magic as long as the DI container doesn't do lots of other things that factory couldn't solve.

Edit: misspelled convenience

   public class MyTest()
   {
      private readonly IServiceProvider _serviceProvider;
      public MyTest(IServiceProvider serviceProvider)
      {
         _serviceProvider = serviceProvider;
      }

      public void MethodA()
      {
         var serviceA = _serviceProvider.GetService<IServiceA>();
      }

      public void MethodB()
      {
         var serviceB = _serviceProvider.GetService<IServiceB>();
      }
   }

The main thing holding C# back is the culture around the DI and weird hostbuilder code associated with ASPNET. If you just skip that part, it's great. Unfortunately a lot of web examples, solutions, and code libraries themselves are ASPNET-focused, and more and more of the code becomes some truly bizarre, unreadable framework injection in an inside-out fluent builder.

I find it very useful for several purposes that have nothing to do with mocking or testing.

> and have become blind to just how much extra code it generates

It doesn’t generate any extra code at all.

For the record, I think that built-in .NET DI is pretty bad. It would be better if they managed to avoid including that abstraction in the framework, even if I personally choose to use DI in most of my projects.

I’ve also used Autofac in projects where it was already in place - I don’t hate it but I like DryIoc better.

When I think DI, I think: //Startup.cs has all the config "goo" I don't want to repeat elsewhere.

services.AddDbContext<MyDbContext>(o=>o.UseSqlServer(config.GetConnectionString("foo"));

services.AddTransient<MyService>();

//MyController.cs (or Page, etc) and others get to use it with no ceremony:

public MyController(MyService foo){ this.foo = foo; }

vs no DI, where the config "goo" has to be repeated in every place I intend to use it (or in this case it could also be buried in MyService.cs):

public MyController(){this.foo = new MyService(new MyDbContext(ConfigurationManager.GetConnectionString("foo")));}

public Dispose(){this.foo.Dispose();}

If I knew MyService would never be swapped out and only ever used in one place, I may opt for the no-DI route. I'll often start there then move it to DI when I want testability, reuse of config, plugability, etc..

The method could return a MyService, or an IMyService if you want to be more flexible. It can always create a fresh object, manage and return a singleton object, or manage a pool of objects. For the new and pool cases, you can have another static method for 'returning' the object when the controller/page is done with it, so you can manage disposal or pool availability.

The biggest advantage I see to this approach is in debugging: there is a clear stack trace back to the source of the object, and also to its implementation if you're not using an interface. With DI you often can't tell where an object came from, and sometimes it takes some digging to even find out its exact type (unless you only have one implementation of each interface, which is often the case.)

No registration or configuration is needed, because the types are hard coded. If you need mocking support, a single IsTest config setting could be used in a conditional statement to determine which implementation to return.

That's very little additional coding if you use a ternary statement, and it lets you opt-in to the mocking mechanism if/when/where you need it, instead of permiating your entire architecture with it.

What you do instead is just:

public static IMyService myService;

public static IMyService getMyService() { if myService return myService; else if(isInTest()) return mockedMyService; else return new MyProdService(wtv); }

And call that in your controller that needs to use MyService.

This is different in that it's static. You don't add a service to it, it creates it the first time you ask for it (if singleton), or everytime you ask for it (otherwise), or pools it, etc.

I recon some similarities, but most enterprise "service locator" involve a lot more than this, and often are meant to give you this runtime dynamism where you can load and unload services as the app is running, etc. making them way more complex for apps that don't care about this.

var service = Startup.getMyService();

And potentially know if the controller should dispose service.

This doesn't seem much less "in the way" or "massive" than:

services.AddSingleton<IMyService,MyService>();

  public void ConfigureServices(IServiceCollection services)
  {
      services.AddScoped<IMyDependency, MyDependency>();
  }

Outside of ASP.Net (console app for example) you can either do this manually, or you can get a ServiceCollection object from the framework, or you ca nuse a 3rd party DI library, etc.

Generally speaking if you don't configure this correctly you get a pretty simple message telling you that the container could not service the request for an IMyDependency or whatever and then it's pretty simple to figure out what you missed in the wire-up.

Edit: Also as others have noted, constructor injection is the way to do DI.

For our multi-tiered system, this means managing caching and logging of certain calls and events at the level of data access. And at the service level, it means dealing with things like authorisation.

Smart use of DI sets the system up in a way were it's easy to handle these types of cross-cutting concerns where appropriate, and with minimal boilerplate. It also simplifies refactoring.

Do you just want to `new SomeClass()` instead? If so, what's stopping you from just doing that?

Duh! Then how’d you wire up interfaces with implementation aka constructor injection?

Construction injection is a type of DI, and it's optional, you don't have to use it.

edit: for clarity

That sounds like dogmatism, and I'm going to take a special note of the emotionally charged language you're using here; it's symptom of some of the underlying issues I see in our industry (more to be said on this).

That said, I do agree with the sentiment in general, but you can (and sometimes should) use the `new` keyword in your code, especially when writing tests. In some cases, it makes testing so much easier and helps with the maintainability.

"I hope you'll not reply-with saying "don't write unit tests"

After 2 decades in this profession, the only think I'm sure of is there is no "silver bullet". Of course, as a general rule, it's a good idea to have a test coverage of your codebase but sometimes it's not valuable and not worth adding it. So it's a "it depends" from me!

A massive waste of time? Adding a constructor and one line to startup.cs is a massive waste of time? Just how long does it take you?

> It's also something that if you're not working regularly with it can be very mysterious and when it fails, fails at run-time, quite inscrutably sometimes.

If DI fails it’s usually just because you’ve forgotten to add that one line to the startup.cs, and the error you get will tell you that. Can you give me a concrete example of how DI is inscrutable?

Passing required dependencies by constructors makes this extremely apparent, not just to the DI framework but to the developers themselves. With constructor injection I can immediately grasp exactly what dependencies an object depends on without even going into the full code flow to look at all the code to find all the IOC container calls.

Edit: Also constructor injection is critical for testing dependency injection. IT allows you to have automated tests that construct every relevant object using the same DI setup as your live application and you can verify that the DI framework can resolve dependencies for everything.

If your DI is lazily done this cannot happen unless you explicitly call all code flows, opening yourself up to runtime errors that may be missed. Unit tests won't catch this because the dependencies of your production site will be different than the dependencies of your test scenarios.

(https://blog.ploeh.dk/2010/02/03/ServiceLocatorisanAnti-Patt...)

Dependency Injection Frameworks have the same issues: - understanding what is going on is harder than injecting objects by hand. - you have limited control over object lifetimes (when objects are created and disposed). Permanent, scoped and transient might be enough most of the time for a web service, but as soon as you fire off tasks that can outlive the requests or when you use it in different circumstances like UI it’s getting a problem.

We are currently on a long term process of migrating a large C++ codebase from a service locator model to just passing dependencies through constructors. New code is significantly simpler to both use, understand and test.

Personally, I quite like that quite a bit compared to platforms and frameworks where the convention seems instead to be, "RTFM or die (at run time)."

Except in Windows Forms, where the norm is a zero-argument constructor and setting everything via properties, because that approach works with component-based design-time tools. Come to think of it, I think WPF and its descendants do the same.

I've actually worked with C# for over 15 years now and written apps with (in order of age) VBScript, webforms, web services (the MS SOAP stuff), MVC 1, MVC 2, MVC 3, MVC 4, Web API, Web API 2, the OData one I forget the name of and asp.net core. Oh and Silverlight. I've probably missed something. On yeah, WCF. And even WWF! Basically EVERYTHING web-related to C#. Plus enough work in PHP, Python, Ruby, Express, etc. to be able to compare different approaches. And even sometimes VB.net, I've maintained and then migrated entire code-bases from that to C#.

I'm not entirely sure what more familiarity I need?

I'd also note that there are a lot of other people agreeing with my in that thread, almost all of whom show a decent technical understanding. And it's got a lot of upvotes.

But, even if I "misunderstood" or have a "lack of familiarity", that speaks of how poor the design/documentation actually is. If you can so easily shoot yourself in the foot with it, it's not fit for purpose.

Any other reasons you think I might be unqualified to talk about the language I've been using for 15 years?

Just to cover some more bases:

1. I've worked in teams

2. I've worked alone

3. I've made apps from scratch

4. I've maintained large existing code bases

5. I've made enterprise apps, e-commerce apps, BI apps, and even just simple websites

6. Millions of people have used my code

7. Apps I made over a decade ago are still being used today

8. I admit I often forget to floss

You never answered what your actual issue with DI is (the concept, implementation, containers, etc), or what your alternative would be, even though numerous people have asked. That makes your complaint seem largely unfounded or a combination of confusion and lack of experience with DI.

There was no built-in DI container before, you had to use your own like Windsor/Autofac/Ninject/etc, and it wasn't as popular because of it as many people skipped it for smaller/less enterprise projects. I'd say exposing more people do it, even if the built-in DI is rather basic, helped improve many new projects that otherwise might not have chosen to do so.

To me, it's clear that some people love DI. SOME. Use it if you want. I don't want to. Stop dictating what's "good" code to experienced developers.

If it helps you, fine, but it hinders me.

And I’m still not seeing the benefit of all that experience by the way.