chainerror/booksrc/tutorial2.md

Simple Chained String Errors

With relatively small changes and the help of the context() method of the chainerror crate the &str errors are now chained together.

Press the play button in the upper right corner and see the nice debug output.

{{#include ../examples/tutorial2.rs}}
# #[allow(dead_code)]
# mod chainerror {
{{#rustdoc_include ../src/lib.rs:-1}}
# }

What did we do here?

{{#include ../examples/tutorial2.rs:13:15}}

The function context(newerror) stores olderror as the source/cause of newerror along with the Location of the context() call and returns Err(newerror).

? then returns the inner error applying .into(), so that we again have a Err(Box<Error + Send + Sync>) as a result.

The Debug implementation of ChainError<T> (which is returned by context()) prints the Debug of T prefixed with the stored filename and line number.

ChainError<T> in our case is ChainError<&str>.