Adds a new "flyweight" type - a lightweight object

"Flyweights" are a bit of a fusion of anonymous objects and ColdMUD frobs.

They are composed of a sequence of "slots" which behave like
properties, a "delegate" to which verb and property (in case of slot
miss) delegate to, and a "contents" which is a sequence of values.

They are immutable and reference counted, and passed by value like MOO
lists and maps.

They will additionally (future) support a "sealing" function which
makes their contents opaque.

"this", and "caller" can be flyweights.

In the future object/room contents will permit flyweights. And command
matching will permit their return as well.

crates/common/src/lib.rs

@@ -20,9 +20,10 @@ pub use encode::{
 };
 
 pub use var::{
-    v_bool, v_empty_list, v_empty_map, v_empty_str, v_err, v_float, v_int, v_list, v_list_iter,
-    v_map, v_none, v_obj, v_objid, v_str, v_string, Associative, ErrorPack, IndexMode, List, Map,
-    Sequence, Str, Var, Variant, AMBIGUOUS, FAILED_MATCH, NOTHING, SYSTEM_OBJECT,
+    v_bool, v_empty_list, v_empty_map, v_empty_str, v_err, v_float, v_flyweight, v_int, v_list,
+    v_list_iter, v_map, v_map_iter, v_none, v_obj, v_objid, v_str, v_string, Associative,
+    ErrorPack, IndexMode, List, Map, Sequence, Str, Var, Variant, AMBIGUOUS, FAILED_MATCH, NOTHING,
+    SYSTEM_OBJECT,
 };
 pub use var::{Error, Obj, Symbol, VarType};
 

crates/common/src/tasks/events.rs

@@ -12,7 +12,7 @@
 // this program. If not, see <https://www.gnu.org/licenses/>.
 //
 
-use crate::{Obj, Symbol, Var};
+use crate::{Symbol, Var};
 use bincode::{Decode, Encode};
 use std::time::SystemTime;
 
@@ -23,7 +23,7 @@ pub struct NarrativeEvent {
     /// When the event happened, in the server's system time.
     pub timestamp: SystemTime,
     /// The object that authored or caused the event.
-    pub author: Obj,
+    pub author: Var,
     /// The event itself.
     pub event: Event,
 }
@@ -41,7 +41,7 @@ pub enum Event {
 
 impl NarrativeEvent {
     #[must_use]
-    pub fn notify(author: Obj, value: Var, content_type: Option<Symbol>) -> Self {
+    pub fn notify(author: Var, value: Var, content_type: Option<Symbol>) -> Self {
         Self {
             timestamp: SystemTime::now(),
             author,
@@ -54,7 +54,7 @@ impl NarrativeEvent {
         self.timestamp
     }
     #[must_use]
-    pub fn author(&self) -> &Obj {
+    pub fn author(&self) -> &Var {
         &self.author
     }
     #[must_use]

crates/common/src/var/flyweight.rs

@@ -0,0 +1,271 @@
+//! A "flyweight" is a lightweight object type which consists only of a delegate, a set of
+//! "slots" (symbol -> var pairs), a single "contents" value (a list), and an optional sealed/signed
+//! state which makes it opaque.
+//!
+//! It is a reference counted, immutable bucket of slots.
+//! Verbs called on it dispatch to the delegate.  `this`, `caller`, perms etc all resolve to the
+//!  actual flyweight.
+//! Properties are resolved in the slots, then the delegate.
+//! Verbs are resolved in the delegate.
+//!
+//! Type protocol for an unsealed flyweight is a sequence. It behaves like a list around the
+//! contents portion.  The slots are accessed with a property access notation.
+//!
+//! The delegate is visible via the `.delegate` property access.
+//! The slots can be listed with a `.slots` property access.
+//! It is therefore illegal for a slot to have the name `slots` or `delegate`.
+//!
+//! So appending, etc can be done like:
+//! `<  x.delegate, x.slots, {@x, y} >`
+//!
+//! Literal syntax is:
+//!
+//! `< delegate, [ slot -> value, ... ], contents >`
+//!
+//! Setting the secret is done with the `seal(priv-key, secret)` function, which signs the flyweight with a
+//! private key. The flyweight then becomes opaque without calling `unseal(pub-key, secret)` with the
+//! right public key and the correct secret.
+//!
+//! When a flyweight is sealed, `.slots`, and `.delegate` (and literal output) will not
+//! be available without calling `unseal()` with the correct secret.
+//!
+//! The purpose is to support two kinds of scenarios:
+//!    "Lightweight" non-persistent patterns where a full object would be overkill.
+//!    "Capability" style security patterns where the flyweight is a capability to a full object.
+//!
+//!
+//! The structure of the flyweight also resembles an XML/HTML node, with a delegate as the tag name,
+//!  slots as the attributes, and contents as the inner text/nodes.
+
+use crate::Error::E_TYPE;
+use crate::{Error, List, Obj, Sequence, Symbol, Var, Variant};
+use bincode::de::{BorrowDecoder, Decoder};
+use bincode::enc::Encoder;
+use bincode::error::{DecodeError, EncodeError};
+use bincode::{BorrowDecode, Decode, Encode};
+use std::fmt::{Debug, Formatter};
+use std::sync::Arc;
+
+#[derive(Clone, Encode, Decode, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Flyweight(Arc<Inner>);
+
+#[derive(Clone, Hash, PartialOrd, Ord, Eq)]
+struct Inner {
+    delegate: Obj,
+    slots: im::Vector<(Symbol, Var)>,
+    contents: List,
+    /// If `secret` is present it's a string signed with a key-pair that can be used to unseal
+    /// the flyweight.
+    /// The meaning of the key is up to the application.
+    seal: Option<String>,
+}
+
+impl PartialEq for Inner {
+    fn eq(&self, other: &Self) -> bool {
+        // Two flyweights where there are 'secrets' involved are never eq.
+        // To avoid leaking information about the secret.
+        if self.seal.is_some() || other.seal.is_some() {
+            return false;
+        }
+        self.delegate == other.delegate
+            && self.slots == other.slots
+            && self.contents == other.contents
+    }
+}
+
+impl Encode for Inner {
+    fn encode<E: Encoder>(&self, encoder: &mut E) -> Result<(), EncodeError> {
+        self.delegate.encode(encoder)?;
+        self.slots.len().encode(encoder)?;
+        for (k, v) in &self.slots {
+            k.encode(encoder)?;
+            v.encode(encoder)?;
+        }
+        self.contents.encode(encoder)?;
+        self.seal.encode(encoder)
+    }
+}
+
+impl Decode for Inner {
+    fn decode<D: Decoder>(decoder: &mut D) -> Result<Self, DecodeError> {
+        let delegate = Obj::decode(decoder)?;
+        let len = usize::decode(decoder)?;
+        let mut slots = im::Vector::new();
+        for _ in 0..len {
+            let k = Symbol::decode(decoder)?;
+            let v = Var::decode(decoder)?;
+            slots.push_back((k, v));
+        }
+        let contents = List::decode(decoder)?;
+        let seal = Option::<String>::decode(decoder)?;
+        Ok(Self {
+            delegate,
+            slots,
+            contents,
+            seal,
+        })
+    }
+}
+
+impl<'a> BorrowDecode<'a> for Inner {
+    fn borrow_decode<D: BorrowDecoder<'a>>(decoder: &mut D) -> Result<Self, DecodeError> {
+        let delegate = Obj::borrow_decode(decoder)?;
+        let len = usize::borrow_decode(decoder)?;
+        let mut slots = im::Vector::new();
+        for _ in 0..len {
+            let k = Symbol::borrow_decode(decoder)?;
+            let v = Var::borrow_decode(decoder)?;
+            slots.push_back((k, v));
+        }
+        let contents = List::borrow_decode(decoder)?;
+        let seal = Option::<String>::borrow_decode(decoder)?;
+        Ok(Self {
+            delegate,
+            slots,
+            contents,
+            seal,
+        })
+    }
+}
+impl Debug for Flyweight {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        if let Some(_) = &self.0.seal {
+            write!(f, "<sealed flyweight>")
+        } else {
+            write!(
+                f,
+                "<{:?}, {:?}, {:?}>",
+                self.0.delegate, self.0.slots, self.0.contents
+            )
+        }
+    }
+}
+
+impl Flyweight {
+    pub fn mk_flyweight(
+        delegate: Obj,
+        slots: &[(Symbol, Var)],
+        contents: List,
+        seal: Option<String>,
+    ) -> Self {
+        Self(Arc::new(Inner {
+            delegate,
+            slots: slots.into(),
+            contents,
+            seal,
+        }))
+    }
+}
+
+impl Flyweight {
+    /// Return the slot with the given key, if it exists.
+    pub fn get_slot(&self, key: &Symbol) -> Option<&Var> {
+        self.0.slots.iter().find(|(k, _)| k == key).map(|(_, v)| v)
+    }
+
+    pub fn slots(&self) -> &im::Vector<(Symbol, Var)> {
+        &self.0.slots
+    }
+
+    pub fn delegate(&self) -> &Obj {
+        &self.0.delegate
+    }
+
+    pub fn seal(&self) -> Option<&String> {
+        self.0.seal.as_ref()
+    }
+
+    pub fn contents(&self) -> &List {
+        &self.0.contents
+    }
+
+    pub fn is_sealed(&self) -> bool {
+        self.0.seal.is_some()
+    }
+
+    pub fn with_new_contents(&self, new_contents: List) -> Var {
+        let fi = Inner {
+            delegate: self.0.delegate.clone(),
+            slots: self.0.slots.clone(),
+            contents: new_contents,
+            seal: self.0.seal.clone(),
+        };
+        let fl = Flyweight(Arc::new(fi));
+        let variant = Variant::Flyweight(fl);
+        Var::from_variant(variant)
+    }
+}
+
+impl Sequence for Flyweight {
+    fn is_empty(&self) -> bool {
+        self.0.contents.is_empty()
+    }
+
+    fn len(&self) -> usize {
+        self.0.contents.len()
+    }
+
+    fn index_in(&self, value: &Var, case_sensitive: bool) -> Result<Option<usize>, Error> {
+        self.0.contents.index_in(value, case_sensitive)
+    }
+
+    fn contains(&self, value: &Var, case_sensitive: bool) -> Result<bool, Error> {
+        self.0.contents.contains(value, case_sensitive)
+    }
+
+    fn index(&self, index: usize) -> Result<Var, Error> {
+        self.0.contents.index(index)
+    }
+
+    fn index_set(&self, index: usize, value: &Var) -> Result<Var, Error> {
+        let new_contents = self.0.contents.index_set(index, value)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+
+    fn push(&self, value: &Var) -> Result<Var, Error> {
+        let new_contents = self.0.contents.push(value)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+
+    fn insert(&self, index: usize, value: &Var) -> Result<Var, Error> {
+        let new_contents = self.0.contents.insert(index, value)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+
+    fn range(&self, from: isize, to: isize) -> Result<Var, Error> {
+        self.0.contents.range(from, to)
+    }
+
+    fn range_set(&self, from: isize, to: isize, with: &Var) -> Result<Var, Error> {
+        let new_contents = self.0.contents.range_set(from, to, with)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+
+    fn append(&self, other: &Var) -> Result<Var, Error> {
+        let new_contents = self.0.contents.append(other)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+
+    fn remove_at(&self, index: usize) -> Result<Var, Error> {
+        let new_contents = self.0.contents.remove_at(index)?;
+        let Variant::List(new_contents_as_list) = new_contents.variant() else {
+            return Err(E_TYPE);
+        };
+        Ok(self.with_new_contents(new_contents_as_list.clone()))
+    }
+}

crates/common/src/var/list.rs

@@ -24,6 +24,7 @@ use bincode::error::{DecodeError, EncodeError};
 use bincode::{BorrowDecode, Decode, Encode};
 use num_traits::ToPrimitive;
 use std::cmp::max;
+use std::fmt::{Debug, Formatter};
 use std::hash::Hash;
 
 #[derive(Clone)]
@@ -35,6 +36,11 @@ impl List {
         Var::from_variant(Variant::List(List(Box::new(l))))
     }
 
+    pub fn mk_list(values: &[Var]) -> List {
+        let l = im::Vector::from(values.to_vec());
+        List(Box::new(l))
+    }
+
     pub fn iter(&self) -> impl Iterator<Item = Var> + '_ {
         (0..self.len()).map(move |i| self.index(i).unwrap())
     }
@@ -73,6 +79,11 @@ impl List {
     }
 }
 
+impl Debug for List {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?}", self.0)
+    }
+}
 impl Sequence for List {
     fn is_empty(&self) -> bool {
         self.0.is_empty()

crates/common/src/var/mod.rs

@@ -13,6 +13,7 @@
 //
 
 mod error;
+mod flyweight;
 mod list;
 mod map;
 mod obj;
@@ -24,6 +25,7 @@ mod var;
 mod variant;
 
 pub use error::{Error, ErrorPack};
+pub use flyweight::Flyweight;
 pub use list::List;
 pub use map::Map;
 pub use obj::{Obj, AMBIGUOUS, FAILED_MATCH, NOTHING, SYSTEM_OBJECT};
@@ -32,8 +34,8 @@ pub use string::Str;
 use strum::FromRepr;
 pub use symbol::Symbol;
 pub use var::{
-    v_bool, v_empty_list, v_empty_map, v_empty_str, v_err, v_float, v_int, v_list, v_list_iter,
-    v_map, v_none, v_obj, v_objid, v_str, v_string, Var,
+    v_bool, v_empty_list, v_empty_map, v_empty_str, v_err, v_float, v_flyweight, v_int, v_list,
+    v_list_iter, v_map, v_map_iter, v_none, v_obj, v_objid, v_str, v_string, Var,
 };
 pub use variant::Variant;
 
@@ -51,6 +53,7 @@ pub enum VarType {
     TYPE_LABEL = 7, // present only in textdump */
     TYPE_FLOAT = 9,
     TYPE_MAP = 10,
+    TYPE_FLYWEIGHT = 11,
 }
 
 /// Sequence index modes: 0 or 1 indexed.