In some cases, you'd like to declare package level variables from a function call. In this case, you can't check for an error and must panic.

For example, the regexp package has MustCompile that will either return a *regexp.Regexp or panic on invalid regular expression.

The must package provide a Wrap function that will wrap a function that returns an value and error with a function that will return a value or panic.

For example, assume you have written a ring buffer:

type RingBuffer struct {
    size int
}

func New(size int) (*RingBuffer, error) {
    if size <= 0 {
        return nil, fmt.Errorf("size (%d) must be > 0", size)
    }
    r := RingBuffer{size: size}
    return &r, nil
}

But people would like to declare a package lever buffer to use. You can write:

var MustNew = must.Wrap(New)

The N variant (e.g. Wrap2, Wrap3) are generated by gen.go. When you make code changes, run go generate and don't forget to commit mustn.go.

MIT