Completely remove expect as well as unwrap

flutter_ffi_plugin/bin/src/message.dart

@@ -258,12 +258,16 @@ import 'package:rinf/rinf.dart';
           rustPath,
           '''
 #![allow(unused_imports)]
+#![allow(dead_code)]
 
 use crate::tokio;
 use prost::Message;
 use rinf::{send_rust_signal, DartSignal};
+use std::error::Error;
 use std::sync::Mutex;
 use tokio::sync::mpsc::{unbounded_channel, UnboundedReceiver, UnboundedSender};
+
+type Result<T> = std::result::Result<T, Box<dyn Error + Send + Sync>>;
 ''',
           atFront: true,
         );
@@ -287,9 +291,13 @@ pub static ${snakeName.toUpperCase()}_CHANNEL: ${messageName}Cell =
     Mutex::new(None);
 
 impl ${normalizePascal(messageName)} {
-    pub fn get_dart_signal_receiver() -> UnboundedReceiver<DartSignal<Self>> {
-        let mut guard = ${snakeName.toUpperCase()}_CHANNEL.lock()
-            .expect("Could not access the channel lock.");
+    pub fn get_dart_signal_receiver()
+        -> Result<UnboundedReceiver<DartSignal<Self>>> 
+    {       
+        let mut guard =
+            ${snakeName.toUpperCase()}_CHANNEL.lock().map_err(|_| {
+                String::from("Could not acquire the channel lock.")
+            })?;
         if guard.is_none() {
             let (sender, receiver) = unbounded_channel();
             guard.replace((sender, Some(receiver)));
@@ -301,17 +309,20 @@ impl ${normalizePascal(messageName)} {
             // which is now closed.
             let pair = guard
                 .as_ref()
-                .expect("Message channel in Rust not present.");
+                .ok_or("Message channel in Rust not present.")?;
             if pair.0.is_closed() {
                 let (sender, receiver) = unbounded_channel();
                 guard.replace((sender, Some(receiver)));
             }
         }
         let pair = guard
             .take()
-            .expect("Message channel in Rust not present.");
+            .ok_or("Message channel in Rust not present.")?;
         guard.replace((pair.0, None));
-        pair.1.expect("Each Dart signal receiver can be taken only once")
+        let receiver = pair
+            .1
+            .ok_or("Each Dart signal receiver can be taken only once")?;
+        Ok(receiver)
     }
 }
 ''',

flutter_ffi_plugin/example/native/hub/src/sample_functions.rs

@@ -18,11 +18,11 @@ const IS_DEBUG_MODE: bool = false;
 static VECTOR: Mutex<Vec<bool>> = Mutex::const_new(Vec::new());
 
 // Business logic for the counter widget.
-pub async fn tell_numbers() {
+pub async fn tell_numbers() -> Result<()> {
     use messages::counter_number::*;
 
     // Stream getter is generated from a marked Protobuf message.
-    let mut receiver = SampleNumberInput::get_dart_signal_receiver();
+    let mut receiver = SampleNumberInput::get_dart_signal_receiver()?;
     while let Some(dart_signal) = receiver.recv().await {
         // Extract values from the message received from Dart.
         // This message is a type that's declared in its Protobuf file.
@@ -44,6 +44,8 @@ pub async fn tell_numbers() {
         }
         .send_signal_to_dart();
     }
+
+    Ok(())
 }
 
 // Business logic for the fractal image.

flutter_ffi_plugin/template/native/hub/src/common.rs

@@ -0,0 +1,3 @@
+use std::error::Error;
+
+pub type Result<T> = std::result::Result<T, Box<dyn Error + Send + Sync>>;

flutter_ffi_plugin/template/native/hub/src/lib.rs

@@ -1,10 +1,11 @@
 //! This `hub` crate is the
 //! entry point of the Rust logic.
 
+mod common;
 mod messages;
 
 use tokio; // Comment this line to target the web.
-// use tokio_with_wasm::alias as tokio; // Uncomment this line to target the web.
+           // use tokio_with_wasm::alias as tokio; // Uncomment this line to target the web.
 
 rinf::write_interface!();
 
@@ -15,10 +16,14 @@ rinf::write_interface!();
 // use `tokio::task::spawn_blocking`.
 async fn main() {
     use messages::basic::*;
+    tokio::spawn(communicate());
+}
+
+async fn communicate() -> Result<()> {
     // Send signals to Dart like below.
     SmallNumber { number: 7 }.send_signal_to_dart();
     // Get receivers that listen to Dart signals like below.
-    let mut receiver = SmallText::get_dart_signal_receiver();
+    let mut receiver = SmallText::get_dart_signal_receiver()?;
     while let Some(dart_signal) = receiver.recv().await {
         let message: SmallText = dart_signal.message;
         rinf::debug_print!("{message:?}");