feat: add qcell

__concurrent/qcell/Cargo.lock

@@ -0,0 +1,25 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "once_cell"
+version = "1.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da32515d9f6e6e489d7bc9d84c71b060db7247dc035bbe44eac88cf87486d8d5"
+
+[[package]]
+name = "qcell"
+version = "0.1.0"
+dependencies = [
+ "qcell 0.5.0",
+]
+
+[[package]]
+name = "qcell"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e5023f06b72bfa9fbb5ebdbe891f02db9406ba026990e0778f80094bc84f3ac8"
+dependencies = [
+ "once_cell",
+]

__concurrent/qcell/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "qcell"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+qcell = "0.5.0"
+

__concurrent/qcell/src/main.rs

@@ -0,0 +1,16 @@
+use std::rc::Rc;
+use qcell::{QCell, QCellOwner};
+
+// https://docs.rs/qcell/latest/qcell/
+fn main() {
+    let mut owner = QCellOwner::new();
+
+    let item = Rc::new(QCell::new(&owner, Vec::<u8>::new()));
+    let iref = owner.rw(&item);
+    // test(&mut owner, &item);    // Compile error
+    iref.push(1);
+
+    fn test(owner: &mut QCellOwner, item: &Rc<QCell<Vec<u8>>>) {
+        owner.rw(&item).push(2);
+    }
+}