You're right, they are related. One difference is simply lineage. Capabilities come out of the erights / security world (e.g. [0]), while dependency injection comes from the XP / agile / Martin Fowler world. More interesting is that to do capabilities correctly you need some type system extensions, namely capture checking. Essentially, this means you delimit where a program can hold a reference to a value derived from a capability. So if you have a function that allocates memory, you can say "there are no references to any allocated memory outside this function call" and hence no use-after-free bugs. It gives a form of resource management that is simpler than Rust's lifetimes. See [1] and [2]. (Technically it's a modal type system versus Rust's substructural type system.) To my mind it's an obvious thing for Zig to add.
Shameless plug. If you're interested in more on this, for a programmer's rather than academic perspective, this is going into my book [3]. I'm writing the chapter of capability passing right now.
alt Hacker News
You're right, they are related. One difference is simply lineage. Capabilities come out of the erights / security world (e.g. [0]), while dependency injection comes from the XP / agile / Martin Fowler world. More interesting is that to do capabilities correctly you need some type system extensions, namely capture checking. Essentially, this means you delimit where a program can hold a reference to a value derived from a capability. So if you have a function that allocates memory, you can say "there are no references to any allocated memory outside this function call" and hence no use-after-free bugs. It gives a form of resource management that is simpler than Rust's lifetimes. See [1] and [2]. (Technically it's a modal type system versus Rust's substructural type system.) To my mind it's an obvious thing for Zig to add.
Shameless plug. If you're interested in more on this, for a programmer's rather than academic perspective, this is going into my book [3]. I'm writing the chapter of capability passing right now.
Back to writing!
[0]: https://blog.acolyer.org/2016/02/16/capability-myths-demolis...
[1]: https://effekt-lang.org/tour/captures
[2]: https://docs.scala-lang.org/scala3/reference/experimental/cc...
[3]: https://functionalprogrammingstrategies.com/