A cool thing you can do, is to store values of all kinds of types in a big HashMap, basically by storing their TypeId and casting them to Box<dyn Any> (see std::any).
Then you can later retrieve those values by specifying the type (and optionally another ID for storing multiple values of the same type).
So, you can create an API which is used like this:
There’s various ECS storage libraries which also implement such an API. Depending on what you’re doing, you might prefer to use those rather than implementing it yourself, but it’s not too difficult to implement yourself.
Well, you would determine the TypeId of SomeOtherType, then search for that as the key in your HashMap and get back a None, because no entry exists and then you’d hand that back to the user.
I guess, my little usage example should’ve included handling of an Option value…
So, it’s only a runtime error, if you decide to .unwrap() or similar.
A cool thing you can do, is to store values of all kinds of types in a big HashMap, basically by storing their
TypeIdand casting them toBox<dyn Any>(see std::any).Then you can later retrieve those values by specifying the type (and optionally another ID for storing multiple values of the same type).
So, you can create an API which is used like this:
let value = MyType::new(); storage.insert(value); let retrieved = storage.get::<MyType>(); assert_eq!(retrieved, value);There’s various ECS storage libraries which also implement such an API. Depending on what you’re doing, you might prefer to use those rather than implementing it yourself, but it’s not too difficult to implement yourself.
There’s a crate for it too: anymap2
What if I specify the wrong type?
let retrieved = storage.get::<SomeOtherType>();?Is it a runtime error or a compile time error?
To answer my own question: I believe it’s a runtime error: https://doc.rust-lang.org/stable/std/any/trait.Any.html#method.downcast
Well, you would determine the
TypeIdofSomeOtherType, then search for that as the key in your HashMap and get back aNone, because no entry exists and then you’d hand that back to the user.I guess, my little usage example should’ve included handling of an
Optionvalue…So, it’s only a runtime error, if you decide to
.unwrap()or similar.