Clone to closure idiom

README.md

@@ -21,6 +21,7 @@ language.
 * TODO interior mutability - UnsafeCell, Cell, RefCell
 * TODO treating Option like a list
 * TODO `Default` trait
+* [Pass clone to closure](idioms/clone-to-closure.md)
 
 ### Design patterns
 

idioms/clone-to-closure.md

@@ -0,0 +1,33 @@
+# Pass clone to closure
+
+## Description
+
+By default, closures capture their environment by borrowing. Or you can use `move`-closure
+to move environment. However, often you want to give copy of some data to closure.
+Use variable rebinding in separate scope for that.
+
+
+## Example
+
+```rust
+let mut num = Rc::new(5);
+let closure = {
+	let num = num.clone();
+	move || {
+		*num + 10
+	}
+};
+
+// Instead of
+let num_copy = num.clone();
+let closure = move || { *num_copy + 10 };
+```
+
+
+## Advantages
+
+Copied data are grouped together with closure definition, so their purpose is more clear
+and they will be dropped immediately even if they are not consumed by closure.
+
+Closure uses same variable names as surrounding code whether data are copied or moved.
+