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However, in accepting such obligations, You may act only + on Your own behalf and on Your sole responsibility, not on behalf + of any other Contributor, and only if You agree to indemnify, + defend, and hold each Contributor harmless for any liability + incurred by, or claims asserted against, such Contributor by reason + of your accepting any such warranty or additional liability. + + END OF TERMS AND CONDITIONS + + APPENDIX: How to apply the Apache License to your work. + + To apply the Apache License to your work, attach the following + boilerplate notice, with the fields enclosed by brackets "[]" + replaced with your own identifying information. (Don't include + the brackets!) The text should be enclosed in the appropriate + comment syntax for the file format. We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + + Copyright 2023 Tasko Olevski + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. \ No newline at end of file diff --git a/README.md b/README.md new file mode 100644 index 0000000..3c7e155 --- /dev/null +++ b/README.md @@ -0,0 +1,65 @@ +# eh (Escape Hatch) + +Succinct error handling for Go inspired by Rust. `eh` can help you avoid the usual Go error +handling boileplate. + +This library tries to provide similar functionality to Rust's Result enum and +the `?` operator. + +For example turn this: + +```go +func example(aFile string) []byte, error { + f, err := os.Open(aFile) + if err != nil { + return nil, err + } + buff := make([]byte, 5) + _, err := f.Read(b1) + if err != nil { + return nil, err + } + return buff, nil +} +``` + +Into this: + +```go +func example(aFile string) (res Result[[]byte]) { + defer EscapeHatch(&res) // must have pointer to the named output Result + buff := make([]byte, 5) + file := NewResult(os.Open(aFile)).ReturnIfErr().Ok + NewResult(file.Read(buff)).ReturnIfErr() + return Result[[]byte]{Ok: buff} +} +``` + +When an error occurs (for example if the file does not exist) this is what happens: + +``` +{Ok:[] Err:open non-existent-file.md: no such file or directory} +``` + +For a successful operation the output is like this: + +``` +{Ok:[60 33 100 111 99 116 121 112] Err: } +``` + +The library provides just a handful or public structs and functions: +- `Result` structs to capture an outcome that can potentially result in an error +- `ReturnIfErr` function (`?` was not possible) that will stop the current function from executing + if there is an error and return a `Result` that contains the error. +- `EscapeHatch` function that should be deferred and given access to the enclosing + function named `Result` argument so that the error can be recovered and the + enclosed function can be interrupted early if an error occurs. + +## Instructions + +A few simple steps to incorporate in your code: +1. Return a named `Result` from your fuction +2. `defer` the `EscapeHatch` function with pointer to the named `Result` argument +3. Wrap functions that return `any, error` into `eh.NewResult` to get `Result` +4. Call `ReturnIfErr()` on any `Result` to stop the execution if there is an error + and return `Result{Err: Error}` from the enclosing function. diff --git a/eh.go b/eh.go new file mode 100644 index 0000000..6c8a608 --- /dev/null +++ b/eh.go @@ -0,0 +1,64 @@ +// Copyright © 2023 Tasko Olevski +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +// Package eh (escapehatch) provides Rust-like error handling in Go. +package eh + +// Result represents a struct that contains an error in the Err field +// or the valid output from some action in the Ok field. Since Results are copied it is +// reccomended that the Ok value be a pointer. +type Result[T any] struct { + Ok T + Err error +} + +// NewResult creates a Result from any value and an error. You can use this to +// convert the output of any function that returns a value and an error. +func NewResult[T any](val T, err error) Result[T] { + return Result[T]{val, err} +} + +// ReturnIfErr checks if there is an error in the result and if so then it will +// panic with the error that was encountered. +func (r Result[T]) ReturnIfErr() Result[T] { + if r.Err != nil { + panic(Error{r.Err}) + } + return r +} + +// Error is used to wrap any errors that are raised because of calling +// ReturnIfErr on a Result. +type Error struct { + WrappedErr error +} + +func (e Error) Error() string { + return e.Error() +} + +// EscapeHatch will recover from a panic that was raised from any error +// raised from the error checks performed by eh. The recovered error is +// populated in the Result pointed by the res pointer. If the recovered +// error was not raised by eh then the same panic will be raised. +func EscapeHatch[T any](res *Result[T]) { + if r := recover(); r != nil { + err, ok := r.(Error) + if !ok { + // Panicking again because the recovered panic is not an Error + panic(r) + } + *res = Result[T]{Err: err.WrappedErr} + } +} diff --git a/eh_test.go b/eh_test.go new file mode 100644 index 0000000..2fc6cbb --- /dev/null +++ b/eh_test.go @@ -0,0 +1,151 @@ +// Copyright © 2023 Tasko Olevski +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +package eh + +import ( + "fmt" + "os" + "sync" + "testing" +) + +func divide(x int, y int) (int, error) { + if y == 0 { + return 0, fmt.Errorf("divide by zero") + } + return x / y, nil +} + +func doDivide(x int, y int) (res Result[int]) { + defer EscapeHatch(&res) + res = NewResult(divide(x, y)).ReturnIfErr() + return res +} + +func doDivideMultiple(x int, y int) (res Result[int]) { + defer EscapeHatch(&res) + res = NewResult(divide(x, y)).ReturnIfErr() + res = NewResult(divide(x*2, y+2)).ReturnIfErr() + return res +} + +func doDivideGoRoutine(x int, y int, res *Result[int], wg *sync.WaitGroup) { + defer wg.Done() + defer EscapeHatch(res) + *res = NewResult(divide(x, y)).ReturnIfErr() +} + +func doDividePtr(x int, y int) (res *Result[int]) { + defer EscapeHatch(res) + ares := NewResult(divide(x, y)).ReturnIfErr() + return &ares +} + +func TestSimple(t *testing.T) { + res := doDivide(4, 2) + if res.Err != nil { + t.FailNow() + } + if res.Ok != 2 { + t.FailNow() + } + res = doDivide(1, 0) + if res.Err == nil { + t.FailNow() + } + if res.Ok != 0 { + t.FailNow() + } +} + +func TestSimpleResultPointer(t *testing.T) { + res := doDivide(4, 2) + if res.Err != nil { + t.FailNow() + } + if res.Ok != 2 { + t.FailNow() + } + res = doDivide(1, 0) + if res.Err == nil { + t.FailNow() + } + if res.Ok != 0 { + t.FailNow() + } +} + +func TestGoRoutines(t *testing.T) { + res1 := Result[int]{} + res2 := Result[int]{} + res3 := Result[int]{} + wg := sync.WaitGroup{} + wg.Add(3) + go doDivideGoRoutine(4, 2, &res1, &wg) + go doDivideGoRoutine(4, 0, &res2, &wg) + go doDivideGoRoutine(5, 0, &res3, &wg) + wg.Wait() + if res1.Ok != 2 { + t.Fatalf("Res1.Ok != 2, it equals %v", res1.Ok) + } + if res2.Err == nil { + t.Fatalf("Res2.Err != nil, result: %+v", res2) + } + if res3.Err == nil { + t.Fatalf("Res3.Err != nil, result: %+v", res3) + } +} + +func TestSimpleResultMultipleOk(t *testing.T) { + res := doDivideMultiple(4, 2) + if res.Err != nil { + t.Fatalf("Error should be nil but is %+v", res) + } + if res.Ok != 2 { + t.Fatalf("Ok has unexpected value %+v", res) + } +} + +func TestSimpleResultMultipleFail(t *testing.T) { + res := doDivideMultiple(4, 0) + if res.Err == nil { + t.Fatalf("Error should not be nil but is %+v", res) + } + if res.Ok != 0 { + t.Fatalf("Ok has unexpected value %+v", res) + } +} + +func example(aFile string) (res Result[[]byte]) { + defer EscapeHatch(&res) + buff := make([]byte, 5) + file := NewResult(os.Open(aFile)).ReturnIfErr().Ok + NewResult(file.Read(buff)).ReturnIfErr() + return Result[[]byte]{Ok: buff} +} + +func TestExample(t *testing.T) { + res := example("README.md") + if res.Err != nil { + t.Fatalf("Err is not nil %+v", res) + } +} + +func TestExampleFail(t *testing.T) { + res := example("non-existing-file") + if res.Err == nil { + t.Fatalf("Err should be nil %+v", res) + } +} diff --git a/go.mod b/go.mod new file mode 100644 index 0000000..d0b131a --- /dev/null +++ b/go.mod @@ -0,0 +1,3 @@ +module github.com/olevski/eh + +go 1.20