Prematurely optimize RoomBuffer's memory usage

Cargo.toml

@@ -44,6 +44,7 @@ libc = "0.2.148"
 log = "0.4.20"
 nonempty = { version = "0.8.1", features = ["serialize"] }
 signal-hook = "0.3.17"
+smallvec = "1.11.1"
 
 # Matrix
 matrix-sdk = { git = "https://github.com/matrix-org/matrix-rust-sdk.git", rev = "91e7f2f7224b8ada17ab639d60da10dad98aeaf9", features = ["eyre", "markdown"] }

src/app.rs

@@ -158,7 +158,7 @@ impl App {
     for client in &self.clients {
       for room in client.joined_rooms() {
         self.buffers.push(Box::new(RoomBuffer::new(
-          vec![client.clone()],
+          [client.clone()],
           room.room_id().to_owned(),
         )));
       }

src/buffers/room.rs

@@ -17,17 +17,23 @@
 use matrix_sdk::ruma::OwnedRoomId;
 use matrix_sdk::Client;
 use matrix_sdk::Room;
+use smallvec::SmallVec;
 
 use super::Buffer;
 
 pub struct RoomBuffer {
-  clients: Vec<Client>,
+  // It's unlikely users will join the same room with more than one account;
+  // avoid a useless heap allocation for the usual case.
+  clients: SmallVec<[Client; 1]>,
   room_id: OwnedRoomId,
 }
 
 impl RoomBuffer {
-  pub fn new(clients: Vec<Client>, room_id: OwnedRoomId) -> Self {
-    RoomBuffer { clients, room_id }
+  pub fn new<Clients: IntoIterator<Item = Client>>(clients: Clients, room_id: OwnedRoomId) -> Self {
+    RoomBuffer {
+      clients: clients.into_iter().collect(),
+      room_id,
+    }
   }
 }