errorx

Calling Close() on an io.WriteCloser can return an important error encountered while flushing to disk. Don't risk missing them by using a plain defer w.Close(). Use errorx.Defer to capture the return value.

package main

import (
	"fmt"

	"github.com/carlmjohnson/errorx"
)

type closer struct{}

func (c closer) Close() error {
	return fmt.Errorf("<had problem closing!>")
}

func openThingie() (c closer, err error) { return }

// Calling Close() on an io.WriteCloser can return an important error
// encountered while flushing to disk. Don't risk missing them by
// using a plain defer w.Close(). Use errorx.Defer to capture the return value.
func main() {
	// If you just defer a close call, you can miss an error
	return1 := func() error {
		thing, err := openThingie()
		if err != nil {
			return err
		}
		defer thing.Close() // oh no, this returned an error!
		// do stuff...
		return nil
	}()
	fmt.Println(return1) // == <nil>

	// Use errorx.Defer and a named return to capture the error
	return2 := func() (err error) {
		thing, err := openThingie()
		if err != nil {
			return err
		}
		defer errorx.Defer(&err, thing.Close)
		// do stuff...
		return nil
	}()
	fmt.Println(return2) // == <had problem closing!>

}

Output:

<nil>
<had problem closing!>

package main

import (
	"fmt"

	"github.com/carlmjohnson/errorx"
)

func main() {
	maybePanic := func(throws bool) (err error) {
		defer errorx.Recover(&err)

		if throws {
			panic("ahhh!")
		}
		return nil
	}

	err := maybePanic(false)
	fmt.Printf("error 1: %v\n", err)

	err = maybePanic(true)
	fmt.Printf("error 2: %v\n", err)

}

Output:

error 1: <nil>
error 2: panic: ahhh!

package main

import (
	"errors"
	"fmt"

	"github.com/carlmjohnson/errorx"
)

func traceErr1(ok bool) (err error) {
	defer errorx.Trace(&err)
	if !ok {
		return errors.New("oh no!")
	}
	return nil
}

func traceErr2(x, y int) (err error) {
	defer errorx.Trace(&err)
	if x+y > 1 {
		return errors.New("uh oh!")
	}
	return nil
}

func main() {
	fmt.Println(traceErr1(true))
	fmt.Println(traceErr1(false))
	fmt.Println(traceErr2(1, -1))
	fmt.Println(traceErr2(1, 1))
}

Output:

<nil>
@github.com/carlmjohnson/errorx_test.traceErr1 (trace_example_test.go:13)
oh no!
<nil>
@github.com/carlmjohnson/errorx_test.traceErr2 (trace_example_test.go:21)
uh oh!