Design by Interface vs IoC/DI

Question

For a long time I've been designing applications using Interface/Inheritance based polymorphism, to gain loosely coupled code. As far as I can see (so far) DI frameworks/IoC merely provide tools to make this "easier", however, the additional level of abstraction seems to be redundant and costs you additional overhead.

The only reason I can think of is if a large team already know a particular DI/IoC framework then everyone can be on the same page.

From my perspective, DI seems to be doing the same thing as design by interface, I hope there's more to it than that, could anyone explain to me why using a DI/IoC framework is a better strategy?

I really hope I've got it wrong about DI/IoC.

Answer 1

Firstly, can you read this required reading and edit in any missing points from there...

If you're expecting DI containers to a) be extraordinary complex beasts or b) a whole new design paradigm, I reckon you're reacting in the normal defensive way one approaches an over-hyped concept.

While one can invest a lot of effort into using DI containers in all sorts of arcane ways, and there's lots of power in there wrt overlaps with AOP etc., the typical sweet spot is for straightforward auto-wiring of dependencies without any "all the team needing to understand" anything or "overhead" (do you mean conceptual or perf? If the latter, have you measured the impact in an actual app?).

But do understand this:- the freedom and focus on clean design enabled by the reduction in friction and increased malleability resulting from you chucking away a lot of boilerplate code (and the necessity to rejig it if things change) IOC containers are for me a critical part of a development ecosystem. While they're only doing a few news here and there, their impact is not in proportion with the actual (small) bit of work they're doing.

As for whether they're different to normal interface based programming and good design principles, I'd view them as something much smaller - a tool that enables just one of the SOLID principles.