X-Git-Url: https://git.chrismorgan.info/anymap/blobdiff_plain/bf29e608d91175d0fca2108fd1b5d75596a4a796..8bc7c76088639ab3a65a642f5d79ce20ef20e2f4:/README.md

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+++ b/README.md
@@ -14,18 +14,19 @@ What this means is that in an ``AnyMap`` you may store zero or one values for ev
 
 This library uses a fair bit of unsafe code for several reasons:
 
-- To support Any and CloneAny, unsafe code is required (because of how the `downcast` methods are defined in `impl dyn Any` rather than being trait methods; I think this is kind of a historical detail of the structure of `std::any::Any`); if you wanted to ditch `Clone` support this unsafety could be removed.
+- To support `CloneAny`, unsafe code is required (because the downcast methods are defined on `dyn Any` rather than being trait methods); if you wanted to ditch `Clone` support this unsafety could be removed.
 
-- In the interests of performance, skipping various checks that are unnecessary because of the invariants of the data structure (no need to check the type ID when it’s been statically ensured by being used as the hash map key) and simplifying hashing (type IDs are already good hashes, no need to mangle them through SipHash).
+- In the interests of performance, skipping various checks that are unnecessary because of the invariants of the data structure (no need to check the type ID when it’s been statically ensured by being used as the hash map key).
 
-It’s not possible to remove all unsafety from this library without also removing some of the functionality. Still, at the cost of the `CloneAny` functionality, the raw interface and maybe the concurrency support, you can definitely remove all unsafe code. Here’s how you could do it:
+- In the `Clone` implementation of `dyn CloneAny` with `Send` and/or `Sync` auto traits added, an unsafe block is used where safe code used to be used in order to avoid a [spurious future-compatibility lint](https://github.com/rust-lang/rust/issues/51443#issuecomment-421988013).
 
-- Remove the genericness of it all;
+It’s not possible to remove all unsafety from this library without also removing some of the functionality. Still, at the cost of the `CloneAny` functionality and the raw interface, you can definitely remove all unsafe code. Here’s how you could do it:
+
+- Remove the genericness of it all (choose `dyn Any`, `dyn Any + Send` or `dyn Any + Send + Sync` and stick with it);
 - Merge `anymap::raw` into the normal interface, flattening it;
-- Change things like `.map(|any| unsafe { any.downcast_unchecked() })` to `.and_then(|any| any.downcast())` (performance cost: one extra superfluous type ID comparison, indirect);
-- Ditch the `TypeIdHasher` since transmuting a `TypeId` is right out (cost: SIP mangling of a u64 on every access).
+- Change things like `.map(|any| unsafe { any.downcast_unchecked() })` to `.and_then(|any| any.downcast())` (performance cost: one extra superfluous type ID comparison, indirect).
 
-Yeah, the performance costs of going safe are quite small. The more serious matters are the loss of `Clone` and maybe `Send + Sync`.
+Yeah, the performance costs of going safe are quite small. The more serious matter is the loss of `Clone`.
 
 But frankly, if you wanted to do all this it’d be easier and faster to write it from scratch. The core of the library is actually really simple and perfectly safe, as can be seen in [`src/lib.rs` in the first commit](https://github.com/chris-morgan/anymap/tree/a294948f57dee47bb284d6a3ae1b8f61a902a03c/src/lib.rs) (note that that code won’t run without a few syntactic alterations; it was from well before Rust 1.0 and has things like `Any:'static` where now we have `Any + 'static`).