With Context-Generic Programming (CGP), there is a way to get around the coherence restriction through a provider trait, and have overlapping implementations in safe, stable Rust. I have a proof of concept implementation of example in the article here: https://gist.github.com/soareschen/d37d74b26ecd0709517a80a3f...
For those who are new to the concept, in a nutshell, CGP allows you to bypass the coherence restrictions in traits/typeclasses, and define multiple overlapping and generic implementations for each CGP trait. As a consequence, when you define a new type, you need to specifically choose an implementation to be used with that type. This is called a wiring step, where you choose the provider implementations for your context.
On the surface, this addition doesn't seem significant. However, it opens up a world of possibilities for enabling powerful design patterns that are based on trait implementations that are named, generic, and overlappable. One of the greatest strengths of CGP is to enable safe, zero-cost, compile-time dispatching through the trait system to accomplish the things that in OOP would typically require dynamic dispatch with runtime errors.
As of 2025, CGP remains in its early stages of development. While promising, it still has several rough edges, particularly in areas such as documentation, tooling, debugging techniques, community support, and ecosystem maturity.
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At this stage, CGP is best suited for early adopters and potential contributors who are willing to experiment and help shape its future.
Clever work. I'm glad to see Rust is at the AbstractSingletonProxyFactoryBean stage of its lifecycle.
Look: patterns like this might unblock people locally but they point to a gap between what people want to say and what the base language allows them to express. In the long term, it's better to expand the language than devise increasingly heroic workarounds for syntactic sclerosis.
On the surface, this addition doesn't seem significant. However, it opens up a world of possibilities for enabling powerful design patterns that are based on trait implementations that are named, generic, and overlappable. One of the greatest strengths of CGP is to enable safe, zero-cost, compile-time dispatching through the trait system to accomplish the things that in OOP would typically require dynamic dispatch with runtime errors.