A Go package that provides breadth-first error search utilities.
It extends the standard errors.As semantics to traverse error trees breadth-first instead of depth-first.

• Breadth-first traversal of wrapped error trees
• Works with both Unwrap() error and Unwrap() []error
• Compatible with Go’s errors.As and custom As(any) bool methods
• Ideal for finding “higher-level” causes before deep leaves

The following example will set e as customErr{"target"}

func ExampleAsType() {
	err := fmt.Errorf("wrap 1: %w",
		fmt.Errorf("wrap 2: %w",
			customErr{"target too deep"},
		),
	)
	err2 := fmt.Errorf("wrap 1: %w", customErr{"target"})

	if e, ok := bfserr.AsType[customErr](errors.Join(err, err2)); ok {
		fmt.Println("found:", e)
	}
}

go get github.com/Brian-Williams/bfserr

If you can use errors.As you should. In most common error trees it will outperform bfserr.AsType.

In the case where you need a bfs of an error tree this will have comparable or better performance to errors.

BenchmarkAs-10                   8333600               121.9 ns/op
BenchmarkAsType-10               7887480               149.2 ns/op
BenchmarkAsDeep-10               5703589               203.5 ns/op            40 B/op          2 allocs/op
BenchmarkAsTypeDeep-10          12341869                96.14 ns/op          104 B/op          4 allocs/op