From a558c35ba4d97ddfcb12718f6ac640292f13cfa2 Mon Sep 17 00:00:00 2001
From: Harald Hoyer <harald@hoyer.xyz>
Date: Tue, 12 Mar 2019 16:43:53 +0100
Subject: [PATCH] make ChainError Send + Sync

---
 README.md              |  4 ++--
 booksrc/tutorial10.md  |  2 +-
 booksrc/tutorial2.md   |  2 +-
 booksrc/tutorial9.md   |  2 +-
 examples/example.rs    |  4 ++--
 examples/tutorial1.rs  |  8 +++----
 examples/tutorial10.rs |  6 ++---
 examples/tutorial11.rs |  6 ++---
 examples/tutorial12.rs |  6 ++---
 examples/tutorial13.rs |  4 ++--
 examples/tutorial2.rs  |  8 +++----
 examples/tutorial3.rs  |  8 +++----
 examples/tutorial4.rs  |  8 +++----
 examples/tutorial5.rs  |  8 +++----
 examples/tutorial6.rs  | 10 ++++----
 examples/tutorial7.rs  |  8 +++----
 examples/tutorial8.rs  |  8 +++----
 examples/tutorial9.rs  |  8 +++----
 src/lib.rs             | 53 +++++++++++++++++++++---------------------
 tests/test_iter.rs     |  6 ++---
 20 files changed, 84 insertions(+), 85 deletions(-)

diff --git a/README.md b/README.md
index 71a829d..9252c1d 100644
--- a/README.md
+++ b/README.md
@@ -48,12 +48,12 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func3() -> Result<(), Box<Error>> {
+fn func3() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
diff --git a/booksrc/tutorial10.md b/booksrc/tutorial10.md
index eb92ff2..84fc436 100644
--- a/booksrc/tutorial10.md
+++ b/booksrc/tutorial10.md
@@ -8,7 +8,7 @@ a `std::error::Error`.
 Not using `String` errors anymore, the `cherr!()` macro seen in the beginning of
 the tutorial has to be used again.
 
-Only returning `Func1ErrorKind` in `func1()` now let us get rid of `Result<(), Box<Error>>` and we can
+Only returning `Func1ErrorKind` in `func1()` now let us get rid of `Result<(), Box<Error + Send + Sync>>` and we can
 use `ChainResult<(), Func1ErrorKind>`.
 
 In `main` we can now directly use the methods of `ChainError<T>` without downcasting the error first.
diff --git a/booksrc/tutorial2.md b/booksrc/tutorial2.md
index 4629605..e217291 100644
--- a/booksrc/tutorial2.md
+++ b/booksrc/tutorial2.md
@@ -24,7 +24,7 @@ along with the filename (`file!()`) and line number (`line!()`)
 and returns `newerror`.
 
 `Err()?` then returns the inner error applying `.into()`, so that we
-again have a `Err(Box<Error>)` as a result.
+again have a `Err(Box<Error + Send + Sync>)` as a result.
 
 The `Debug` implementation of `ChainError<T>` (which is returned by `cherr!()`)
 prints the `Debug` of `T` prefixed with the stored filename and line number.
diff --git a/booksrc/tutorial9.md b/booksrc/tutorial9.md
index df2e292..4027cdc 100644
--- a/booksrc/tutorial9.md
+++ b/booksrc/tutorial9.md
@@ -7,7 +7,7 @@ In this example `func1()` can return either `Func1ErrorFunc2` or `Func1ErrorIO`.
 We might want to `match` on `func1()` with something like:
 
 ~~~rust,ignore
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     match func1() {
         Err(e) if let Some(s) = e.downcast_chain_ref::<Func1ErrorIO>() =>
         eprintln!("Func1ErrorIO:\n{:?}", s),
diff --git a/examples/example.rs b/examples/example.rs
index 3d97f70..8aadc8d 100644
--- a/examples/example.rs
+++ b/examples/example.rs
@@ -3,12 +3,12 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func3() -> Result<(), Box<Error>> {
+fn func3() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
diff --git a/examples/tutorial1.rs b/examples/tutorial1.rs
index 87778d9..d296a92 100644
--- a/examples/tutorial1.rs
+++ b/examples/tutorial1.rs
@@ -2,25 +2,25 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(_) = do_some_io() {
         Err("func2 error")?;
     }
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(_) = func2() {
         Err("func1 error")?;
     }
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     func1()
 }
diff --git a/examples/tutorial10.rs b/examples/tutorial10.rs
index b22d0b7..15eae31 100644
--- a/examples/tutorial10.rs
+++ b/examples/tutorial10.rs
@@ -3,14 +3,14 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
 derive_str_cherr!(Func2Error);
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     Ok(())
@@ -39,7 +39,7 @@ fn func1() -> ChainResult<(), Func1ErrorKind> {
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         match e.kind() {
             Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
diff --git a/examples/tutorial11.rs b/examples/tutorial11.rs
index 46cf00c..00e3d74 100644
--- a/examples/tutorial11.rs
+++ b/examples/tutorial11.rs
@@ -3,14 +3,14 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
 derive_str_cherr!(Func2Error);
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     Ok(())
@@ -45,7 +45,7 @@ fn func1() -> ChainResult<(), Func1ErrorKind> {
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         match e.kind() {
             Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
diff --git a/examples/tutorial12.rs b/examples/tutorial12.rs
index a20fede..8cdc8aa 100644
--- a/examples/tutorial12.rs
+++ b/examples/tutorial12.rs
@@ -3,14 +3,14 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
 derive_str_cherr!(Func2Error);
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     Ok(())
@@ -54,7 +54,7 @@ fn handle_func1errorkind(e: &Func1ErrorKind) {
     }
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         match *e {
             Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
diff --git a/examples/tutorial13.rs b/examples/tutorial13.rs
index 6c30358..9cfe090 100644
--- a/examples/tutorial13.rs
+++ b/examples/tutorial13.rs
@@ -2,14 +2,14 @@ pub mod mycrate {
     use chainerror::*;
     use std::io;
 
-    fn do_some_io() -> std::result::Result<(), Box<std::error::Error>> {
+    fn do_some_io() -> std::result::Result<(), Box<std::error::Error + Send + Sync>> {
         Err(io::Error::from(io::ErrorKind::NotFound))?;
         Ok(())
     }
 
     derive_str_cherr!(Func2Error);
 
-    fn func2() -> std::result::Result<(), Box<std::error::Error>> {
+    fn func2() -> std::result::Result<(), Box<std::error::Error + Send + Sync>> {
         let filename = "foo.txt";
         do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
         Ok(())
diff --git a/examples/tutorial2.rs b/examples/tutorial2.rs
index d75f0a4..349c5cd 100644
--- a/examples/tutorial2.rs
+++ b/examples/tutorial2.rs
@@ -4,25 +4,25 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = do_some_io() {
         Err(cherr!(e, "func2 error"))?;
     }
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func2() {
         Err(cherr!(e, "func1 error"))?;
     }
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     func1()
 }
diff --git a/examples/tutorial3.rs b/examples/tutorial3.rs
index 6915a62..cdbffed 100644
--- a/examples/tutorial3.rs
+++ b/examples/tutorial3.rs
@@ -4,22 +4,22 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     do_some_io().map_err(|e| cherr!(e, "func2 error"))?;
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(|e| cherr!(e, "func1 error"))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         eprintln!("{:?}", e);
     }
diff --git a/examples/tutorial4.rs b/examples/tutorial4.rs
index de51745..d037215 100644
--- a/examples/tutorial4.rs
+++ b/examples/tutorial4.rs
@@ -3,23 +3,23 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(mstrerr!("func1 error"))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         eprintln!("{:?}", e);
     }
diff --git a/examples/tutorial5.rs b/examples/tutorial5.rs
index e6f36f3..4d673e3 100644
--- a/examples/tutorial5.rs
+++ b/examples/tutorial5.rs
@@ -3,18 +3,18 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func2() {
         if let Some(s) = e.source() {
             eprintln!("func2 failed because of '{}'", s);
@@ -24,7 +24,7 @@ fn func1() -> Result<(), Box<Error>> {
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         eprintln!("{}", e);
     }
diff --git a/examples/tutorial6.rs b/examples/tutorial6.rs
index aca48b4..22e0e78 100644
--- a/examples/tutorial6.rs
+++ b/examples/tutorial6.rs
@@ -3,26 +3,26 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(mstrerr!("func1 error"))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         eprintln!("Error: {}", e);
-        let mut s = e.as_ref();
+        let mut s : &(dyn Error) = e.as_ref();
         while let Some(c) = s.source() {
             if let Some(ioerror) = c.downcast_ref::<io::Error>() {
                 eprintln!("caused by: std::io::Error: {}", ioerror);
diff --git a/examples/tutorial7.rs b/examples/tutorial7.rs
index 3cb3d2c..bf09449 100644
--- a/examples/tutorial7.rs
+++ b/examples/tutorial7.rs
@@ -3,23 +3,23 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
     Ok(())
 }
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(mstrerr!("func1 error"))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         eprintln!("Error: {}", e);
         if let Some(s) = e.downcast_chain_ref::<String>() {
diff --git a/examples/tutorial8.rs b/examples/tutorial8.rs
index 831e6ed..be92df7 100644
--- a/examples/tutorial8.rs
+++ b/examples/tutorial8.rs
@@ -3,14 +3,14 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
 derive_str_cherr!(Func2Error);
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     Ok(())
@@ -18,12 +18,12 @@ fn func2() -> Result<(), Box<Error>> {
 
 derive_str_cherr!(Func1Error);
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         if let Some(f1err) = e.downcast_chain_ref::<Func1Error>() {
             eprintln!("Func1Error: {}", f1err);
diff --git a/examples/tutorial9.rs b/examples/tutorial9.rs
index f1954d3..d9436f4 100644
--- a/examples/tutorial9.rs
+++ b/examples/tutorial9.rs
@@ -3,14 +3,14 @@ use std::error::Error;
 use std::io;
 use std::result::Result;
 
-fn do_some_io() -> Result<(), Box<Error>> {
+fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     Err(io::Error::from(io::ErrorKind::NotFound))?;
     Ok(())
 }
 
 derive_str_cherr!(Func2Error);
 
-fn func2() -> Result<(), Box<Error>> {
+fn func2() -> Result<(), Box<Error + Send + Sync>> {
     let filename = "foo.txt";
     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     Ok(())
@@ -19,14 +19,14 @@ fn func2() -> Result<(), Box<Error>> {
 derive_str_cherr!(Func1ErrorFunc2);
 derive_str_cherr!(Func1ErrorIO);
 
-fn func1() -> Result<(), Box<Error>> {
+fn func1() -> Result<(), Box<Error + Send + Sync>> {
     func2().map_err(mstrerr!(Func1ErrorFunc2, "func1 error calling func2"))?;
     let filename = "bar.txt";
     do_some_io().map_err(mstrerr!(Func1ErrorIO, "Error reading '{}'", filename))?;
     Ok(())
 }
 
-fn main() -> Result<(), Box<Error>> {
+fn main() -> Result<(), Box<Error + Send + Sync>> {
     if let Err(e) = func1() {
         if let Some(s) = e.downcast_ref::<ChainError<Func1ErrorIO>>() {
             eprintln!("Func1ErrorIO:\n{:?}", s);
diff --git a/src/lib.rs b/src/lib.rs
index dd1471c..2107335 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -32,18 +32,18 @@
 //! use std::io;
 //! use std::result::Result;
 //!
-//! fn do_some_io() -> Result<(), Box<Error>> {
+//! fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
 //!     Err(io::Error::from(io::ErrorKind::NotFound))?;
 //!     Ok(())
 //! }
 //!
-//! fn func2() -> Result<(), Box<Error>> {
+//! fn func2() -> Result<(), Box<Error + Send + Sync>> {
 //!     let filename = "foo.txt";
 //!     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
 //!     Ok(())
 //! }
 //!
-//! fn func1() -> Result<(), Box<Error>> {
+//! fn func1() -> Result<(), Box<Error + Send + Sync>> {
 //!     func2().map_err(mstrerr!("func1 error"))?;
 //!     Ok(())
 //! }
@@ -74,12 +74,12 @@
 //! use std::io;
 //! use std::result::Result;
 //!
-//! fn do_some_io() -> Result<(), Box<Error>> {
+//! fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
 //!     Err(io::Error::from(io::ErrorKind::NotFound))?;
 //!     Ok(())
 //! }
 //!
-//! fn func3() -> Result<(), Box<Error>> {
+//! fn func3() -> Result<(), Box<Error + Send + Sync>> {
 //!     let filename = "foo.txt";
 //!     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
 //!     Ok(())
@@ -175,7 +175,6 @@
     macro_use_extern_crate,
     missing_debug_implementations,
     missing_docs,
-    trivial_casts,
     trivial_numeric_casts,
     unused_extern_crates,
     unused_import_braces,
@@ -201,7 +200,7 @@ pub struct ChainError<T> {
     #[cfg(not(feature = "no-fileline"))]
     occurrence: Option<&'static str>,
     kind: T,
-    error_cause: Option<Box<dyn Error + 'static>>,
+    error_cause: Option<Box<dyn Error + 'static + Send + Sync>>,
 }
 
 /// convenience type alias
@@ -213,7 +212,7 @@ impl<T: 'static + Display + Debug> ChainError<T> {
     #[inline]
     pub fn new(
         kind: T,
-        error_cause: Option<Box<dyn Error + 'static>>,
+        error_cause: Option<Box<dyn Error + 'static + Send + Sync>>,
         occurrence: Option<&'static str>,
     ) -> Self {
         Self {
@@ -228,7 +227,7 @@ impl<T: 'static + Display + Debug> ChainError<T> {
     #[inline]
     pub fn new(
         kind: T,
-        error_cause: Option<Box<dyn Error + 'static>>,
+        error_cause: Option<Box<dyn Error + 'static + Send + Sync>>,
         _occurrence: Option<&'static str>,
     ) -> Self {
         Self { kind, error_cause }
@@ -248,14 +247,14 @@ impl<T: 'static + Display + Debug> ChainError<T> {
     /// # use std::error::Error;
     /// # use std::io;
     /// # use std::result::Result;
-    /// fn do_some_io() -> Result<(), Box<Error>> {
+    /// fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
     ///     Ok(())
     /// }
     ///
     /// derive_str_cherr!(Func2Error);
     ///
-    /// fn func2() -> Result<(), Box<Error>> {
+    /// fn func2() -> Result<(), Box<Error + Send + Sync>> {
     ///     let filename = "foo.txt";
     ///     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     ///     Ok(())
@@ -263,7 +262,7 @@ impl<T: 'static + Display + Debug> ChainError<T> {
     ///
     /// derive_str_cherr!(Func1Error);
     ///
-    /// fn func1() -> Result<(), Box<Error>> {
+    /// fn func1() -> Result<(), Box<Error + Send + Sync>> {
     ///     func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
     ///     Ok(())
     /// }
@@ -353,14 +352,14 @@ impl<T: 'static + Display + Debug> ChainError<T> {
     /// # use std::error::Error;
     /// # use std::io;
     /// # use std::result::Result;
-    /// fn do_some_io() -> Result<(), Box<Error>> {
+    /// fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
     ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
     ///     Ok(())
     /// }
     ///
     /// derive_str_cherr!(Func2Error);
     ///
-    /// fn func2() -> Result<(), Box<Error>> {
+    /// fn func2() -> Result<(), Box<Error + Send + Sync>> {
     ///     let filename = "foo.txt";
     ///     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
     ///     Ok(())
@@ -539,21 +538,21 @@ impl ChainErrorDown for dyn Error + 'static + Send + Sync {
 impl<T: 'static + Display + Debug> Error for ChainError<T> {
     #[inline]
     fn source(&self) -> Option<&(dyn Error + 'static)> {
-        self.error_cause.as_ref().map(|e| e.as_ref())
+        self.error_cause.as_ref().map(|e| e.as_ref() as &(dyn Error + 'static))
     }
 }
 
 impl<T: 'static + Display + Debug> Error for &ChainError<T> {
     #[inline]
     fn source(&self) -> Option<&(dyn Error + 'static)> {
-        self.error_cause.as_ref().map(|e| e.as_ref())
+        self.error_cause.as_ref().map(|e| e.as_ref() as &(dyn Error + 'static))
     }
 }
 
 impl<T: 'static + Display + Debug> Error for &mut ChainError<T> {
     #[inline]
     fn source(&self) -> Option<&(dyn Error + 'static)> {
-        self.error_cause.as_ref().map(|e| e.as_ref())
+        self.error_cause.as_ref().map(|e| e.as_ref() as &(dyn Error + 'static))
     }
 }
 
@@ -714,7 +713,7 @@ macro_rules! into_cherr {
 /// #         }
 /// #     }
 /// # }
-/// fn do_some_stuff() -> Result<(), Box<Error>> {
+/// fn do_some_stuff() -> Result<(), Box<Error + Send + Sync>> {
 ///     Err(io::Error::from(io::ErrorKind::NotFound))?;
 ///     Ok(())
 /// }
@@ -772,17 +771,17 @@ macro_rules! mcherr {
 /// # use std::error::Error;
 /// # use std::io;
 /// # use std::result::Result;
-/// # fn do_some_io() -> Result<(), Box<Error>> {
+/// # fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
 /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
 /// #     Ok(())
 /// # }
-/// fn func2() -> Result<(), Box<Error>> {
+/// fn func2() -> Result<(), Box<Error + Send + Sync>> {
 ///     let filename = "foo.txt";
 ///     do_some_io().map_err(mstrerr!("Error reading '{}'", filename))?;
 ///     Ok(())
 /// }
 ///
-/// fn func1() -> Result<(), Box<Error>> {
+/// fn func1() -> Result<(), Box<Error + Send + Sync>> {
 ///     func2().map_err(mstrerr!("func1 error"))?;
 ///     Ok(())
 /// }
@@ -813,13 +812,13 @@ macro_rules! mcherr {
 /// # use std::error::Error;
 /// # use std::io;
 /// # use std::result::Result;
-/// # fn do_some_io() -> Result<(), Box<Error>> {
+/// # fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
 /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
 /// #     Ok(())
 /// # }
 /// derive_str_cherr!(Func2Error);
 ///
-/// fn func2() -> Result<(), Box<Error>> {
+/// fn func2() -> Result<(), Box<Error + Send + Sync>> {
 ///     let filename = "foo.txt";
 ///     do_some_io().map_err(mstrerr!(Func2Error, "Error reading '{}'", filename))?;
 ///     Ok(())
@@ -827,7 +826,7 @@ macro_rules! mcherr {
 ///
 /// derive_str_cherr!(Func1Error);
 ///
-/// fn func1() -> Result<(), Box<Error>> {
+/// fn func1() -> Result<(), Box<Error + Send + Sync>> {
 ///     func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
 ///     Ok(())
 /// }
@@ -883,7 +882,7 @@ macro_rules! mstrerr {
 ///
 /// derive_str_cherr!(Func1Error);
 ///
-/// fn func1() -> Result<(), Box<Error>> {
+/// fn func1() -> Result<(), Box<Error + Send + Sync>> {
 ///     func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
 ///     Ok(())
 /// }
@@ -931,7 +930,7 @@ macro_rules! strerr {
 /// # use std::error::Error;
 /// # use std::io;
 /// # use std::result::Result;
-/// # fn do_some_io() -> Result<(), Box<Error>> {
+/// # fn do_some_io() -> Result<(), Box<Error + Send + Sync>> {
 /// #     Err(io::Error::from(io::ErrorKind::NotFound))?;
 /// #     Ok(())
 /// # }
@@ -945,7 +944,7 @@ macro_rules! strerr {
 ///
 /// derive_str_cherr!(Func1Error);
 ///
-/// fn func1() -> Result<(), Box<Error>> {
+/// fn func1() -> Result<(), Box<Error + Send + Sync>> {
 ///     func2().map_err(mstrerr!(Func1Error, "func1 error"))?;
 ///     Ok(())
 /// }
diff --git a/tests/test_iter.rs b/tests/test_iter.rs
index c351160..c451f7f 100644
--- a/tests/test_iter.rs
+++ b/tests/test_iter.rs
@@ -4,7 +4,7 @@ use std::fmt::Write;
 use std::io;
 
 #[test]
-fn test_iter() -> Result<(), Box<Error>> {
+fn test_iter() -> Result<(), Box<Error + Send + Sync>> {
     let err = io::Error::from(io::ErrorKind::NotFound);
     let err = cherr!(err, "1");
     let err = cherr!(err, "2");
@@ -31,7 +31,7 @@ fn test_iter() -> Result<(), Box<Error>> {
 }
 
 #[test]
-fn test_find_cause() -> Result<(), Box<Error>> {
+fn test_find_cause() -> Result<(), Box<Error + Send + Sync>> {
     let err = io::Error::from(io::ErrorKind::NotFound);
     let err = cherr!(err, "1");
     let err = cherr!(err, "2");
@@ -48,7 +48,7 @@ fn test_find_cause() -> Result<(), Box<Error>> {
 }
 
 #[test]
-fn test_root_cause() -> Result<(), Box<Error>> {
+fn test_root_cause() -> Result<(), Box<Error + Send + Sync>> {
     let err = io::Error::from(io::ErrorKind::NotFound);
     let err = cherr!(err, "1");
     let err = cherr!(err, "2");