20 releases (11 breaking)
0.11.0 | Nov 9, 2021 |
---|---|
0.10.0 | Feb 13, 2019 |
0.9.2 | Feb 15, 2018 |
0.9.1 | Sep 16, 2017 |
0.2.1 | Oct 26, 2015 |
#362 in Rust patterns
1,889,961 downloads per month
Used in 886 crates
(17 directly)
16KB
301 lines
downcast
A trait (& utilities) for downcasting trait objects back to their original types.
link to API documentation
example usage
Add to your Cargo.toml:
[dependencies]
downcast = "0.12"
Add to your crate root:
#[macro_use]
extern crate downcast;
- simple showcases the most simple usage of this library.
- with_params showcases how to deal with traits who have type parameters.
- sync_service showcases how to downcast
Arc
-pointers.
build features
- std (default) enables all functionality requiring the standard library (
Downcast::downcast()
). - nightly enables all functionality requiring rust nightly (
Any::type_name()
).
faq
Q: I'm getting the size for values of type XXX cannot be known at compile time
errors, what am i doing wrong?
A: Make sure you use the corresponding Any
bound along with the Downcast
traits. So, Any
for Downcast
and AnySync
for DowncastSync
.
Q: Can i cast trait objects to trait objects?
A: No, that is currently no possible in safe rust - and unsafe solutions are very tricky, as well. If you found a solution, feel free to share it!
Q: What is the difference between this and the downcast-rs
crate on crates.io?
A: At the moment, there isn't one, really. There was an unfortunate naming clash. You may consider using the other crate, as it is more actively maintained. This one is considered feature-complete and frozen in functionality. Hopefully, one day, the Rust language will make downcasting easier and we will need neither of these crates anymore!