Comment by Toutouxc
9 months ago
AFAIK composition, in the traditional sense, means that you put your objects/concepts together from different smaller objects or concepts. Composition would be to have a struct Car that uses another struct called Engine to handle its driving needs. A car “has a” engine. A trait that implements the “this thing has an engine” behavior isn’t composition, it’s actually much closer to [multiple] inheritance (a car “is a” motorized vehicle).
Traits do implement interface inheritance, but that doesn't have the same general drawbacks as implementation inheritance (such as the well-known "fragile base class" problem).
I don't know the terminology. I just know that Rust does whatever the alternative is to the Java way with inheritance. You don't get stuck with the classic classification problem.