I think you're confusing composition with aggregation. DI can't be composition because the injected object is shared/borrowed, strong composition on the other hand requires the object to be owned. A composed child does not exist without its parent.

[–] RedFrank24@piefed.social 1 points 10 hours ago* (last edited 10 hours ago) (1 children)

Only if you're going by the strict UML definition of composition, which doesn't really apply here, since the industry has moved on a bit since UML was king.

Either way, you can use DI to do composition in the strictest UML way, provided every single dependency is transient and creates a new instance every single time. Even then though, when most devs talk about composition, they aren't referring to the strict UML definition.

[–] aaaaaaaaargh@feddit.org 1 points 8 hours ago

Yeah but I was talking about the opposite. I can clearly spot composition in many frontend framework such as react or flutter but e.g. spring DI is a different thing to me.