refactor(core): small improvements

* remove excessive unsafe code in `MessageVTable::lookup()`
* more accurate unsafe comments
* remove obsolete hack `Message::_touch()`
* `ResponseToken::forget()` consume `self`
* avoid needless pointer casts

elfo-core/src/envelope.rs

@@ -31,7 +31,7 @@ assert_eq_size!(Envelope, usize);
 // TODO: the current size (on x86-64) is 64 bytes, but it can be reduced.
 // And... it should be reduced once `TraceId` is extended to 16 bytes.
 pub(crate) struct EnvelopeHeader {
-    /// See [`mailbox.rs`] for more details.
+    /// See `mailbox.rs` for more details.
     pub(crate) link: mailbox::Link,
     created_time: Instant, // Now used also as a sent time.
     trace_id: TraceId,
@@ -237,7 +237,7 @@ impl Envelope {
         let message_offset = self.header().message_offset;
 
         // SAFETY: `message_offset` refers to the same allocation object.
-        let ptr = unsafe { self.0.as_ptr().cast::<u8>().add(message_offset as usize) };
+        let ptr = unsafe { self.0.as_ptr().byte_add(message_offset as usize) };
 
         // SAFETY: `envelope_repr_layout()` guarantees that `ptr` is valid.
         unsafe { NonNull::new_unchecked(ptr.cast()) }
@@ -271,7 +271,10 @@ impl Envelope {
         // SAFETY: `self` is properly initialized.
         let header = unsafe { self.0.as_mut() };
 
-        if let MessageKind::RequestAny(token) | MessageKind::RequestAll(token) = &mut header.kind {
+        let fake_kind = MessageKind::Regular { sender: Addr::NULL };
+        let kind = mem::replace(&mut header.kind, fake_kind);
+
+        if let MessageKind::RequestAny(token) | MessageKind::RequestAll(token) = kind {
             // FIXME: probably invalid for ALL requests, need to decrement remainder.
             // REVIEW: DO NOT forget check & fix it before merging.
             token.forget();

elfo-core/src/exec.rs

@@ -40,7 +40,7 @@ impl ExecResult for () {
 impl ExecResult for never::Never {
     #[allow(private_interfaces)]
     fn unify(self) -> Result<(), BoxedError> {
-        unreachable!()
+        self
     }
 }
 

elfo-core/src/mailbox.rs

@@ -136,7 +136,7 @@ impl Mailbox {
     pub(crate) async fn recv(&self) -> RecvResult {
         loop {
             // TODO: it should be possible to use `dequeue_unchecked()` here.
-            // Preliminarily, we should guarantee that `recv()` can be called only
+            // Preliminarily, we should guarantee that it can be called only
             // by one consumer. However, it's not enough to create a dedicated
             // `MailboxConsumer` because users can steal `Context` to another
             // task/thread and create a race with the `drop_all()` method.

elfo-core/src/message.rs

@@ -74,12 +74,6 @@ pub trait Message:
         Self::_type_id() == type_id
     }
 
-    // Called in `_read()` and `_write()` to avoid
-    // * [rust#47384](https://github.com/rust-lang/rust/issues/47384)
-    // * [rust#99721](https://github.com/rust-lang/rust/issues/99721)
-    #[doc(hidden)]
-    fn _touch(&self);
-
     #[doc(hidden)]
     #[inline(always)]
     fn _into_any(self) -> AnyMessage {
@@ -122,9 +116,7 @@ pub trait Message:
     #[inline(always)]
     unsafe fn _read(ptr: NonNull<MessageRepr>) -> Self {
         let data_ref = &ptr.cast::<MessageRepr<Self>>().as_ref().data;
-        let data = ptr::read(data_ref);
-        data._touch();
-        data
+        ptr::read(data_ref)
     }
 
     /// # Safety
@@ -137,7 +129,6 @@ pub trait Message:
     #[doc(hidden)]
     #[inline(always)]
     unsafe fn _write(self, ptr: NonNull<MessageRepr>) {
-        self._touch();
         let repr = MessageRepr::new(self);
         ptr::write(ptr.cast::<MessageRepr<Self>>().as_ptr(), repr);
     }

elfo-core/src/message/any.rs

@@ -229,9 +229,6 @@ impl Message for AnyMessage {
         true
     }
 
-    #[inline(always)]
-    fn _touch(&self) {}
-
     #[inline(always)]
     fn _into_any(self) -> AnyMessage {
         self
@@ -431,16 +428,14 @@ impl<'a> AnyMessageRef<'a> {
     pub fn downcast_ref<M: Message>(&self) -> Option<&'a M> {
         let ret = self.inner.downcast_ref();
 
-        // SAFETY: we produce lifetime bound to the original one.
-        // Note: semantically it's shortening not extending.
+        // SAFETY: we produce lifetime bound to the original `AnyMessage` or `Envelope`.
         unsafe { mem::transmute::<Option<&M>, Option<&'a M>>(ret) }
     }
 
     pub(crate) unsafe fn downcast_ref_unchecked<M: Message>(&self) -> &'a M {
         let ret = self.inner.downcast_ref_unchecked();
 
-        // SAFETY: we produce lifetime bound to the original one.
-        // Note: semantically it's shortening not extending.
+        // SAFETY: we produce lifetime bound to the original `AnyMessage` or `Envelope`.
         unsafe { mem::transmute::<&M, &'a M>(ret) }
     }
 }

elfo-core/src/message/repr.rs

@@ -1,5 +1,7 @@
 use std::{
-    alloc, fmt,
+    alloc,
+    borrow::Borrow,
+    fmt,
     ptr::{self, NonNull},
 };
 
@@ -69,8 +71,9 @@ impl PartialEq for MessageTypeId {
 #[repr(C)]
 // It's `pub` only because used in private methods of `AnyMessage`.
 // Actually, it's not reexported at all.
+#[derive(Clone)]
 #[doc(hidden)]
-pub struct MessageRepr<M = ()> {
+pub struct MessageRepr<M = Erased> {
     pub(crate) vtable: &'static MessageVTable,
     pub(crate) data: M,
 }
@@ -88,18 +91,13 @@ impl<M: Message> MessageRepr<M> {
     }
 }
 
+// Actually, it's not reexported at all.
+#[doc(hidden)]
+pub struct Erased;
+
 // Protection against footgun.
 assert_not_impl_any!(MessageRepr: Clone);
 
-impl<M: Message> Clone for MessageRepr<M> {
-    fn clone(&self) -> Self {
-        Self {
-            vtable: self.vtable,
-            data: self.data.clone(),
-        }
-    }
-}
-
 // === MessageVTable ===
 
 /// Message Virtual Table.
@@ -269,28 +267,27 @@ mod vtablefns {
 #[linkme::distributed_slice]
 pub static MESSAGE_VTABLES_LIST: [&'static MessageVTable] = [..];
 
-static MESSAGE_VTABLES_MAP: Lazy<FxHashMap<(&'static str, &'static str), &'static MessageVTable>> =
-    Lazy::new(|| {
-        MESSAGE_VTABLES_LIST
-            .iter()
-            .map(|vtable| ((vtable.protocol, vtable.name), *vtable))
-            .collect()
-    });
+#[derive(PartialEq, Eq, Hash)]
+pub struct Signature([&'static str; 2]); // [protocol, name]
+
+impl<'a> Borrow<[&'a str; 2]> for Signature {
+    fn borrow(&self) -> &[&'a str; 2] {
+        &self.0
+    }
+}
+
+static MESSAGE_VTABLES_MAP: Lazy<FxHashMap<Signature, &'static MessageVTable>> = Lazy::new(|| {
+    MESSAGE_VTABLES_LIST
+        .iter()
+        .map(|vtable| (Signature([vtable.protocol, vtable.name]), *vtable))
+        .collect()
+});
 
 impl MessageVTable {
     /// Finds a vtable by protocol and name.
     /// Used for deserialization of `AnyMessage` and in networking.
     pub(crate) fn lookup(protocol: &str, name: &str) -> Option<&'static Self> {
-        // Extend lifetimes to static in order to get `(&'static str, &'static str)`.
-        // SAFETY: this pair doesn't overlive the function.
-        let (protocol, name) = unsafe {
-            (
-                std::mem::transmute::<&str, &'static str>(protocol),
-                std::mem::transmute::<&str, &'static str>(name),
-            )
-        };
-
-        MESSAGE_VTABLES_MAP.get(&(protocol, name)).copied()
+        MESSAGE_VTABLES_MAP.get(&[protocol, name]).copied()
     }
 }
 

elfo-core/src/request_table.rs

@@ -251,7 +251,7 @@ impl ResponseToken {
 
     #[doc(hidden)]
     #[inline]
-    pub fn forget(&mut self) {
+    pub fn forget(mut self) {
         self.data = None;
     }
 

elfo-logger/src/line_transaction.rs

@@ -5,7 +5,7 @@ use super::line_buffer::LineBuffer;
 /// This is needed due to rust's closure lifetimes binding limitation. Consider,
 /// for example, the following implementation:
 /// ```no_compile
-/// triat LineFactory<'a>: FnOnce(&'a LineBuffer) -> Self::Line {
+/// trait LineFactory<'a>: FnOnce(&'a LineBuffer) -> Self::Line {
 ///     type Line: Line + 'a;
 /// }
 /// ```

elfo-macros-impl/src/message.rs

@@ -215,9 +215,6 @@ pub fn message_impl(
                 fn _vtable(&self) -> &'static #internal::MessageVTable {
                     VTABLE
                 }
-
-                #[inline(never)]
-                fn _touch(&self) {}
             }
 
             #[#internal::linkme::distributed_slice(#internal::MESSAGE_VTABLES_LIST)]

elfo-network/src/worker/mod.rs

@@ -300,7 +300,7 @@ fn make_network_envelope(
             (sender, trace_id, payload, token)
         }
         // Response
-        (Ok(envelope), Some(mut token)) => {
+        (Ok(envelope), Some(token)) => {
             let sender = envelope.sender();
             let trace_id = envelope.trace_id();
             let (message, kind) = envelope.unpack::<AnyMessage>().expect("impossible");
@@ -323,7 +323,7 @@ fn make_network_envelope(
             (sender, trace_id, payload, None)
         }
         // Failed/Ignored Response
-        (Err(err), Some(mut token)) => {
+        (Err(err), Some(token)) => {
             let sender = Addr::NULL;
             let trace_id = token.trace_id();