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Module: stdgo.errors

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Overview

Index

Variables

import stdgo.errors.Errors
var errUnsupported:stdgo.Error

Classes

import stdgo.errors.*

class Errors

Package errors implements functions to manipulate errors.

The [New] function creates errors whose only content is a text message.

An error e wraps another error if e's type has one of the methods 

    	Unwrap() error
    	Unwrap() []error

If e.Unwrap() returns a non-nil error w or a slice containing w, then we say that e wraps w. A nil error returned from e.Unwrap() indicates that e does not wrap any error. It is invalid for an Unwrap method to return an []error containing a nil error value.

An easy way to create wrapped errors is to call [fmt.Errorf] and apply the %w verb to the error argument: 

    	wrapsErr := fmt.Errorf("... %w ...", ..., err, ...)

Successive unwrapping of an error creates a tree. The [Is] and [As] functions inspect an error's tree by examining first the error itself followed by the tree of each of its children in turn (pre-order, depth-first traversal).

Is examines the tree of its first argument looking for an error that matches the second. It reports whether it finds a match. It should be used in preference to simple equality checks: 

    	if errors.Is(err, fs.ErrExist)

is preferable to 

    	if err == fs.ErrExist

because the former will succeed if err wraps [io/fs.ErrExist].

As examines the tree of its first argument looking for an error that can be assigned to its second argument, which must be a pointer. If it succeeds, it performs the assignment and returns true. Otherwise, it returns false. The form 

    	var perr *fs.PathError
    	if errors.As(err, &perr) {
    		fmt.Println(perr.Path)
}

is preferable to 

    	if perr, ok := err.(*fs.PathError); ok {
    		fmt.Println(perr.Path)
}

because the former will succeed if err wraps an [*io/fs.PathError].

Errors function as

function as(_err:stdgo.Error, _target:stdgo.AnyInterface):Bool
As finds the first error in err's tree that matches target, and if one is found, sets
        target to that error value and returns true. Otherwise, it returns false.

The tree consists of err itself, followed by the errors obtained by repeatedly calling Unwrap. When err wraps multiple errors, As examines err followed by a depth-first traversal of its children.

An error matches target if the error's concrete value is assignable to the value pointed to by target, or if the error has a method As(interface{}) bool such that As(target) returns true. In the latter case, the As method is responsible for setting target.

An error type might provide an As method so it can be treated as if it were a different error type.

As panics if target is not a non-nil pointer to either a type that implements error, or to any interface type.

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Errors function is_

function is_(_err:stdgo.Error, _target:stdgo.Error):Bool

Is reports whether any error in err's tree matches target.

The tree consists of err itself, followed by the errors obtained by repeatedly calling Unwrap. When err wraps multiple errors, Is examines err followed by a depth-first traversal of its children.

An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.

An error type might provide an Is method so it can be treated as equivalent to an existing error. For example, if MyError defines 

        	func (m MyError) Is(target error) bool { return target == fs.ErrExist }

then Is(MyError{}, fs.ErrExist) returns true. See [syscall.Errno.Is] for an example in the standard library. An Is method should only shallowly compare err and the target and not call Unwrap on either.

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Errors function join

function join(_errs:haxe.Rest<stdgo.Error>):stdgo.Error
Join returns an error that wraps the given errors.
        Any nil error values are discarded.
        Join returns nil if every value in errs is nil.
        The error formats as the concatenation of the strings obtained
        by calling the Error method of each element of errs, with a newline
        between each string.

A non-nil error returned by Join implements the Unwrap() []error method.

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Errors function new_

function new_(_text:String):stdgo.Error
New returns an error that formats as the given text.
        Each call to New returns a distinct error value even if the text is identical.

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Errors function unwrap

function unwrap(_err:stdgo.Error):stdgo.Error
Unwrap returns the result of calling the Unwrap method on err, if err's
        type contains an Unwrap method returning error.
        Otherwise, Unwrap returns nil.

Unwrap only calls a method of the form "Unwrap() error". In particular Unwrap does not unwrap errors returned by [Join].

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Typedefs

import stdgo.errors.*

typedef T__interface_0

typedef T__interface_0 = stdgo._internal.errors.T__interface_0;

typedef T__interface_1

typedef T__interface_1 = stdgo._internal.errors.T__interface_1;

typedef T__interface_2

typedef T__interface_2 = stdgo._internal.errors.T__interface_2;

typedef T__interface_3

typedef T__interface_3 = stdgo._internal.errors.T__interface_3;

Abstracts

abstract T_errorString

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abstract T_joinError

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