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deref

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This commit is contained in:
Harald Hoyer 2019-02-03 19:33:26 +01:00
parent 4762a75cfe
commit c9259a3ea3
3 changed files with 39 additions and 7 deletions
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4
booksrc/tutorial12.md
View file

@ -1,7 +1,7 @@
# Deref for the ErrorKind
Because ChainError<T> implements Deref to &T, we can also match on `*e` instead of `e.kind()`.
Because ChainError<T> implements Deref to &T, we can also match on `*e` instead of `e.kind()`
or call a function with `&e`
~~~rust
use crate::chainerror::*;
{{#include ../examples/tutorial12.rs:2:}}

11
examples/tutorial12.rs
View file

@ -45,6 +45,15 @@ fn func1() -> ChainResult<(), Func1ErrorKind> {
Ok(())
}
fn handle_func1errorkind(e: &Func1ErrorKind) {
match e {
Func1ErrorKind::Func2 => eprintln!("Main Error Report: func1 error calling func2"),
Func1ErrorKind::IO(ref filename) => {
eprintln!("Main Error Report: func1 error reading '{}'", filename)
}
}
}
fn main() -> Result<(), Box<Error>> {
if let Err(e) = func1() {
match *e {
@ -54,6 +63,8 @@ fn main() -> Result<(), Box<Error>> {
}
}
handle_func1errorkind(&e);
if let Some(e) = e.find_chain_cause::<Func2Error>() {
eprintln!("\nError reported by Func2Error: {}", e)
}

31
src/lib.rs
View file

@ -263,7 +263,7 @@ impl<T: 'static + Display + Debug> ChainError<T> {
self.iter().filter_map(Error::downcast_ref::<U>).next()
}
/// Find the first error cause of type ChainError<U>, if any exists
/// Find the first error cause of type `ChainError<U>`, if any exists
///
/// Same as `find_cause`, but hides the `ChainError<U>` implementation internals
///
@ -273,7 +273,7 @@ impl<T: 'static + Display + Debug> ChainError<T> {
/// // Instead of writing
/// err.find_cause::<ChainError<FooError>>();
///
/// // leave out the ChainError<T> implementation detail
/// // leave out the ChainError<FooError> implementation detail
/// err.find_chain_cause::<FooError>();
/// ~~~
pub fn find_chain_cause<U: Error + 'static>(&self) -> Option<&ChainError<U>> {
@ -282,8 +282,24 @@ impl<T: 'static + Display + Debug> ChainError<T> {
.next()
}
// FIXME: naming
fn find_chain_or_cause<U: Error + 'static>(&self) -> Option<&U> {
/// Find the first error cause of type `ChainError<U>` or `U`, if any exists and return `U`
///
/// Same as `find_cause` and `find_chain_cause`, but hides the `ChainError<U>` implementation internals
///
/// # Examples
///
/// ~~~rust,ignore
/// // Instead of writing
/// err.find_cause::<ChainError<FooErrorKind>>();
/// // and/or
/// err.find_chain_cause::<FooErrorKind>();
/// // and/or
/// err.find_cause::<FooErrorKind>();
///
/// // leave out the ChainError<FooErrorKind> implementation detail
/// err.find_chain_or_kind::<FooErrorKind>();
/// ~~~
pub fn find_kind_or_cause<U: Error + 'static>(&self) -> Option<&U> {
self.iter()
.filter_map(|e| {
e.downcast_ref::<ChainError<U>>().map(|e| e.kind())
@ -353,6 +369,11 @@ impl<T: 'static + Display + Debug> ChainError<T> {
&self.kind
}
/// Returns an Iterator over all error causes/sources
///
/// # Example
///
///
pub fn iter(&self) -> impl Iterator<Item = &(dyn Error + 'static)> {
ErrorIter {
current: Some(self),
@ -378,7 +399,7 @@ impl<T: 'static + Display + Debug> std::ops::Deref for ChainError<T> {
type Target = T;
fn deref(&self) -> &Self::Target {
self.kind()
&self.kind
}
}