Trait failure::Fail

pub trait Fail: Display + Debug + Send + Sync + 'static {
    fn name(&self) -> Option<&str> { ... }
    fn cause(&self) -> Option<&dyn Fail> { ... }
    fn backtrace(&self) -> Option<&Backtrace> { ... }
    fn context<D>(self, context: D) -> Context<D>
    where
        D: Display + Send + Sync + 'static,
        Self: Sized,
    { ... }
    fn compat(self) -> Compat<Self>
    where
        Self: Sized,
    { ... }
}

The Fail trait.

Implementors of this trait are called 'failures'.

All error types should implement Fail, which provides a baseline of functionality that they all share.

Fail has no required methods, but it does require that your type implement several other traits:

• Display: to print a user-friendly representation of the error.
• Debug: to print a verbose, developer-focused representation of the error.
• Send + Sync: Your error type is required to be safe to transfer to and reference from another thread

Additionally, all failures must be 'static. This enables downcasting.

Fail provides several methods with default implementations. Two of these may be appropriate to override depending on the definition of your particular failure: the cause and backtrace methods.

The failure_derive crate provides a way to derive the Fail trait for your type. Additionally, all types that already implement std::error::Error, and are also Send, Sync, and 'static, implement Fail by a blanket impl.

Provided methods

fn name(&self) -> Option<&str>

Returns the "name" of the error.

This is typically the type name. Not all errors will implement this. This method is expected to be most useful in situations where errors need to be reported to external instrumentation systems such as crash reporters.

fn cause(&self) -> Option<&dyn Fail>

Returns a reference to the underlying cause of this failure, if it is an error that wraps other errors.

Returns None if this failure does not have another error as its underlying cause. By default, this returns None.

This should never return a reference to self, but only return Some when it can return a different failure. Users may loop over the cause chain, and returning self would result in an infinite loop.

fn backtrace(&self) -> Option<&Backtrace>

Returns a reference to the Backtrace carried by this failure, if it carries one.

Returns None if this failure does not carry a backtrace. By default, this returns None.

fn context<D>(self, context: D) -> Context<D> where
    D: Display + Send + Sync + 'static,
    Self: Sized, 

Provides context for this failure.

This can provide additional information about this error, appropriate to the semantics of the current layer. That is, if you have a lower-level error, such as an IO error, you can provide additional context about what that error means in the context of your function. This gives users of this function more information about what has gone wrong.

This takes any type that implements Display, as well as Send/Sync/'static. In practice, this means it can take a String or a string literal, or another failure, or some other custom context-carrying type.

fn compat(self) -> Compat<Self> where
    Self: Sized, 

Wraps this failure in a compatibility wrapper that implements std::error::Error.

This allows failures to be compatible with older crates that expect types that implement the Error trait from std::error.

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Methods

impl dyn Fail

pub fn downcast_ref<T: Fail>(&self) -> Option<&T>

Attempts to downcast this failure to a concrete type by reference.

If the underlying error is not of type T, this will return None.

pub fn downcast_mut<T: Fail>(&mut self) -> Option<&mut T>

Attempts to downcast this failure to a concrete type by mutable reference.

If the underlying error is not of type T, this will return None.

pub fn find_root_cause(&self) -> &dyn Fail

Returns the "root cause" of this Fail - the last value in the cause chain which does not return an underlying cause.

If this type does not have a cause, self is returned, because it is its own root cause.

This is equivalent to iterating over iter_causes() and taking the last item.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f dyn Fail;

pub fn iter_causes(&self) -> Causes

Returns a iterator over the causes of this Fail with the cause of this fail as the first item and the root_cause as the final item.

Use iter_chain to also include the fail itself.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f dyn Fail;

pub fn iter_chain(&self) -> Causes

Returns a iterator over all fails up the chain from the current as the first item up to the root_cause as the final item.

This means that the chain also includes the fail itself which means that it does not start with cause. To skip the outermost fail use iter_causes instead.

pub fn root_cause(&self) -> &dyn Fail

Deprecated since 0.1.2:

please use the 'find_root_cause()' method instead

Deprecated alias to find_root_cause.

Important traits for Causes<'f>

impl<'f> Iterator for Causes<'f> type Item = &'f dyn Fail;

pub fn causes(&self) -> Causes

Deprecated since 0.1.2:

please use the 'iter_chain()' method instead

Deprecated alias to iter_chain.

Trait Implementations

impl AsFail for dyn Fail

fn as_fail(&self) -> &dyn Fail

Converts a reference to Self into a dynamic trait object of Fail.

impl AsRef<dyn Fail + 'static> for Error

fn as_ref(&self) -> &dyn Fail

Performs the conversion.

Implementations on Foreign Types

impl Fail for Box<dyn Fail>

fn cause(&self) -> Option<&dyn Fail>

fn backtrace(&self) -> Option<&Backtrace>

fn name(&self) -> Option<&str>

fn context<D>(self, context: D) -> Context<D> where
    D: Display + Send + Sync + 'static,
    Self: Sized, 

fn compat(self) -> Compat<Self> where
    Self: Sized, 

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Implementors

impl<D: Display + Send + Sync + 'static> Fail for Context<D>

fn name(&self) -> Option<&str>

fn cause(&self) -> Option<&dyn Fail>

fn backtrace(&self) -> Option<&Backtrace>

fn context<D>(self, context: D) -> Context<D> where
    D: Display + Send + Sync + 'static,
    Self: Sized, 

fn compat(self) -> Compat<Self> where
    Self: Sized, 

impl<E: Error + Send + 'static> Fail for SyncFailure<E>

fn name(&self) -> Option<&str>

fn cause(&self) -> Option<&dyn Fail>

fn backtrace(&self) -> Option<&Backtrace>

fn context<D>(self, context: D) -> Context<D> where
    D: Display + Send + Sync + 'static,
    Self: Sized, 

fn compat(self) -> Compat<Self> where
    Self: Sized, 

impl<E: StdError + Send + Sync + 'static> Fail for E

fn name(&self) -> Option<&str>

fn cause(&self) -> Option<&dyn Fail>

fn backtrace(&self) -> Option<&Backtrace>

fn context<D>(self, context: D) -> Context<D> where
    D: Display + Send + Sync + 'static,
    Self: Sized, 

fn compat(self) -> Compat<Self> where
    Self: Sized, 

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