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                        <h1 class="menu-title">chainerror</h1> 

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                        <pre><pre class="playpen"><code class="language-rust">use crate::chainerror::*;
use std::error::Error;
use std::io;
use std::result::Result;

fn do_some_io() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    Err(io::Error::from(io::ErrorKind::NotFound))?;
    Ok(())
}

derive_str_cherr!(Func2Error);

fn func2() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    let filename = &quot;foo.txt&quot;;
    do_some_io().map_err(mstrerr!(Func2Error, &quot;Error reading '{}'&quot;, filename))?;
    Ok(())
}

#[derive(Debug)]
enum Func1Error {
    Func2,
    IO(String),
}

impl ::std::fmt::Display for Func1Error {
    fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
        match self {
            Func1Error::Func2 =&gt; write!(f, &quot;func1 error calling func2&quot;),
            Func1Error::IO(filename) =&gt; write!(f, &quot;Error reading '{}'&quot;, filename),
        }
    }
}

fn func1() -&gt; ChainResult&lt;(), Func1Error&gt; {
    func2().map_err(|e| cherr!(e, Func1Error::Func2))?;
    let filename = String::from(&quot;bar.txt&quot;);
    do_some_io().map_err(|e| cherr!(e, Func1Error::IO(filename)))?;
    Ok(())
}

fn main() -&gt; Result&lt;(), Box&lt;Error&gt;&gt; {
    if let Err(e) = func1() {
        match e.kind() {
            Func1Error::Func2 =&gt; eprintln!(&quot;Main Error Report: func1 error calling func2&quot;),
            Func1Error::IO(filename) =&gt; {
                eprintln!(&quot;Main Error Report: func1 error reading '{}'&quot;, filename)
            }
        }

        if let Some(e) = e.find_chain_cause::&lt;Func2Error&gt;() {
            eprintln!(&quot;Error reported by Func2Error: {}&quot;, e)
        }

        eprintln!(&quot;\nDebug Error:\n{:?}&quot;, e);
    }
    Ok(())
}
# #[allow(dead_code)]
# mod chainerror {
# use std::error::Error;
# use std::fmt::{Debug, Display, Formatter, Result};
# use std::result::Result as StdResult;
# 
# pub struct ChainError&lt;T&gt; {
#     #[cfg(not(feature = &quot;no-fileline&quot;))]
#     occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     kind: T,
#     error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
# }
# 
# pub type ChainResult&lt;O, E&gt; = StdResult&lt;O, ChainError&lt;E&gt;&gt;;
# 
# impl&lt;T: 'static + Display + Debug&gt; ChainError&lt;T&gt; {
#     #[cfg(not(feature = &quot;no-fileline&quot;))]
#     pub fn new(
#         kind: T,
#         error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
#         occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     ) -&gt; Self {
#         Self {
#             occurrence,
#             kind,
#             error_cause,
#         }
#     }
# 
#     #[cfg(feature = &quot;no-fileline&quot;)]
#     pub fn new(
#         kind: T,
#         error_cause: Option&lt;Box&lt;dyn Error + 'static&gt;&gt;,
#         _occurrence: Option&lt;(u32, &amp;'static str)&gt;,
#     ) -&gt; Self {
#         Self { kind, error_cause }
#     }
# 
#     pub fn root_cause(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         let mut cause = self as &amp;(dyn Error + 'static);
#         while let Some(c) = cause.source() {
#             cause = c;
#         }
#         Some(cause)
#     }
# 
#     pub fn find_cause&lt;U: Error + 'static&gt;(&amp;self) -&gt; Option&lt;&amp;U&gt; {
#         let mut cause = self as &amp;(dyn Error + 'static);
#         loop {
#             if cause.is::&lt;U&gt;() {
#                 return cause.downcast_ref::&lt;U&gt;();
#             }
# 
#             match cause.source() {
#                 Some(c) =&gt; cause = c,
#                 None =&gt; return None,
#             }
#         }
#     }
# 
#     pub fn find_chain_cause&lt;U: Error + 'static&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;U&gt;&gt; {
#         let mut cause = self as &amp;(dyn Error + 'static);
#         loop {
#             if cause.is::&lt;ChainError&lt;U&gt;&gt;() {
#                 return cause.downcast_ref::&lt;ChainError&lt;U&gt;&gt;();
#             }
# 
#             match cause.source() {
#                 Some(c) =&gt; cause = c,
#                 None =&gt; return None,
#             }
#         }
#     }
# 
#     pub fn kind&lt;'a&gt;(&amp;'a self) -&gt; &amp;'a T {
#         &amp;self.kind
#     }
# }
# 
# pub trait ChainErrorDown {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool;
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt;;
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt;;
# }
# 
# use std::any::TypeId;
# 
# impl&lt;U: 'static + Display + Debug&gt; ChainErrorDown for ChainError&lt;U&gt; {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         TypeId::of::&lt;T&gt;() == TypeId::of::&lt;U&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         if self.is_chain::&lt;T&gt;() {
#             unsafe { Some(&amp;*(self as *const dyn Error as *const &amp;ChainError&lt;T&gt;)) }
#         } else {
#             None
#         }
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         if self.is_chain::&lt;T&gt;() {
#             unsafe { Some(&amp;mut *(self as *mut dyn Error as *mut &amp;mut ChainError&lt;T&gt;)) }
#         } else {
#             None
#         }
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl ChainErrorDown for dyn Error + 'static + Send + Sync {
#     fn is_chain&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; bool {
#         self.is::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_ref&lt;T: 'static + Display + Debug&gt;(&amp;self) -&gt; Option&lt;&amp;ChainError&lt;T&gt;&gt; {
#         self.downcast_ref::&lt;ChainError&lt;T&gt;&gt;()
#     }
# 
#     fn downcast_chain_mut&lt;T: 'static + Display + Debug&gt;(&amp;mut self) -&gt; Option&lt;&amp;mut ChainError&lt;T&gt;&gt; {
#         self.downcast_mut::&lt;ChainError&lt;T&gt;&gt;()
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for &amp;ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Error for &amp;mut ChainError&lt;T&gt; {
#     fn source(&amp;self) -&gt; Option&lt;&amp;(dyn Error + 'static)&gt; {
#         if let Some(ref e) = self.error_cause {
#             Some(e.as_ref())
#         } else {
#             None
#         }
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Display for ChainError&lt;T&gt; {
#     fn fmt(&amp;self, f: &amp;mut Formatter) -&gt; Result {
#         write!(f, &quot;{}&quot;, self.kind)?;
# 
#         #[cfg(feature = &quot;display-cause&quot;)]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, &quot;\nCaused by:&quot;)?;
#                 Display::fmt(&amp;e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# impl&lt;T: 'static + Display + Debug&gt; Debug for ChainError&lt;T&gt; {
#     fn fmt(&amp;self, f: &amp;mut Formatter) -&gt; Result {
#         #[cfg(not(feature = &quot;no-fileline&quot;))]
#         {
#             if let Some(o) = self.occurrence {
#                 write!(f, &quot;{}:{}: &quot;, o.1, o.0)?;
#             }
#         }
# 
#         Debug::fmt(&amp;self.kind, f)?;
# 
#         #[cfg(not(feature = &quot;no-debug-cause&quot;))]
#         {
#             if let Some(e) = self.source() {
#                 writeln!(f, &quot;\nCaused by:&quot;)?;
#                 Debug::fmt(&amp;e, f)?;
#             }
#         }
#         Ok(())
#     }
# }
# 
# #[macro_export]
# macro_rules! cherr {
#     ( $k:expr ) =&gt; {
#         ChainError::&lt;_&gt;::new($k, None, Some((line!(), file!())))
#     };
#     ( $e:expr, $k:expr ) =&gt; {
#         ChainError::&lt;_&gt;::new($k, Some(Box::from($e)), Some((line!(), file!())))
#     };
# }
# 
# #[macro_export]
# macro_rules! mstrerr {
#     ( $t:ident, $v:expr $(, $more:expr)* ) =&gt; {
#         |e| cherr!(e, $t (format!($v, $( $more , )* )))
#     };
#     ( $t:path, $v:expr $(, $more:expr)* ) =&gt; {
#         |e| cherr!(e, $t (format!($v, $( $more , )* )))
#     };
#     ( $v:expr $(, $more:expr)* ) =&gt; {
#         |e| cherr!(e, format!($v, $( $more , )* ))
#     };
# }
# 
# #[macro_export]
# macro_rules! derive_str_cherr {
#     ($e:ident) =&gt; {
#         struct $e(String);
#         impl ::std::fmt::Display for $e {
#             fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
#                 write!(f, &quot;{}&quot;, self.0)
#             }
#         }
#         impl ::std::fmt::Debug for $e {
#             fn fmt(&amp;self, f: &amp;mut ::std::fmt::Formatter) -&gt; ::std::fmt::Result {
#                 write!(f, &quot;{}({})&quot;, stringify!($e), self.0)
#             }
#         }
#         impl ::std::error::Error for $e {}
#     };
# }
# 
# #[macro_export]
# macro_rules! try_cherr_ref {
#     ( $e:expr, $t:ident ) =&gt; {
#         $e.downcast_ref::&lt;ChainError&lt;$t&gt;&gt;()
#     };
#     ( $e:expr, $t:path ) =&gt; {
#         $e.downcast_ref::&lt;ChainError&lt;$t&gt;&gt;()
#     };
# }
# 
# #[macro_export]
# macro_rules! try_cherr_mut {
#     ( $e:expr, $t:ident ) =&gt; {
#         $e.downcast_mut::&lt;ChainError&lt;$t&gt;&gt;()
#     };
#     ( $e:expr, $t:path ) =&gt; {
#         $e.downcast_mut::&lt;ChainError&lt;$t&gt;&gt;()
#     };
# }
# }
</code></pre></pre>

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