checking if one can mess with the order of .map_err() and .and_then()

andthenchaintest/Cargo.lock

@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "andthenchaintest"
+version = "0.1.0"

andthenchaintest/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "andthenchaintest"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

andthenchaintest/src/main.rs

@@ -0,0 +1,10 @@
+fn main() {
+    let value: Result<u32, u32> = Err(20)
+        .map_err(|_: u32| 30)
+        .and_then(|_old: u32| Err(40));
+
+    // Note: Order does not affect these results; even if `.map_err()` comes before `.and_then()`,
+    // when `.and_then()` returns an error, it is captured by `.map_err()` again.
+
+    println!("{:?}", value);
+}