Illustrating alexcrichton/futures-rs/#676

Makefile

@@ -1,5 +1,4 @@
-CARGO = cargo +$(TOOLCHAIN)
-TOOLCHAIN = nightly
+CARGO = cargo
 
 .PHONY: all bench build check clean doc install publish run test update
 
@@ -9,7 +8,7 @@ bench:
 	@$(CARGO) bench
 
 build:
-	@env TERM=xterm-256color $(CARGO) build --color=always 2>&1; $(CARGO) build 2> cargo.out 1>/dev/null
+	@env TERM=xterm-256color $(CARGO) build --color=always 2>&1
 
 check: build test
 

cargo.out

@@ -1,16 +1,24 @@
    Compiling futuretest v0.1.0 (file:///mnt/c/Users/Mahmoud/git/futuretest)
-error[E0277]: the trait bound `(): futures::Future` is not satisfied
-  --> src/main.rs:17:1
+error[E0271]: type mismatch resolving `<futures::FutureResult<(), std::string::String> as futures::IntoFuture>::Error == &str`
+  --> src/main.rs:12:10
    |
-17 | / fn test() -> MapErr<(), ()> {
-18 | |     future::ok(())
-19 | |         .map_err(|String| ())
-20 | | }
-   | |_^ the trait `futures::Future` is not implemented for `()`
+12 |         .and_then(|_|
+   |          ^^^^^^^^ expected struct `std::string::String`, found &str
    |
-   = note: required by `futures::MapErr`
+   = note: expected type `std::string::String`
+              found type `&str`
 
-error: aborting due to previous error
+error[E0599]: no method named `and_then` found for type `futures::AndThen<futures::MapErr<futures::FutureResult<(), ()>, [closure@src/main.rs:11:18: 11:42]>, futures::FutureResult<(), std::string::String>, [closure@src/main.rs:12:19: 15:14]>` in the current scope
+  --> src/main.rs:17:10
+   |
+17 |         .and_then(|_| future::result::<(), String>(Err("another &'static str error".to_owned())))
+   |          ^^^^^^^^
+   |
+   = note: the method `and_then` exists but the following trait bounds were not satisfied:
+           `futures::AndThen<futures::MapErr<futures::FutureResult<(), ()>, [closure@src/main.rs:11:18: 11:42]>, futures::FutureResult<(), std::string::String>, [closure@src/main.rs:12:19: 15:14]> : futures::Future`
+           `&mut futures::AndThen<futures::MapErr<futures::FutureResult<(), ()>, [closure@src/main.rs:11:18: 11:42]>, futures::FutureResult<(), std::string::String>, [closure@src/main.rs:12:19: 15:14]> : futures::Future`
+
+error: aborting due to 2 previous errors
 
 error: Could not compile `futuretest`.
 

src/main.rs

@@ -1,5 +1,3 @@
-#![feature(conservative_impl_trait)]
-
 extern crate futures;
 extern crate tokio_core;
 use futures::future::{self};
@@ -9,12 +7,15 @@ use tokio_core::reactor::Core;
 fn main() {
     let mut core = Core::new().expect("Failed to initialize tokio_core reactor!");
 
-    let f = test();
+    let f = future::result::<(),()>(Ok(()))
+        .map_err(|_| "&'static str error")
+        .and_then(|_|
+             future::result(Ok(())
+                .map_err(|()| "String error".to_owned())
+            )
+        )
+        .and_then(|_| future::result::<(), String>(Err("another &'static str error".to_owned())))
+    ;
 
     core.run(f).unwrap();
 }
-
-fn test() -> MapErr<(), ()> {
-    future::ok(())
-        .map_err(|String| ())
-}