Proposal: remove panics from context.Get* methods and return errors explicitly

[bkielbasa]

This proposal is connected to #73.

The goal of the proposal is to remove all panics from the context helper methods and return errors explicitly. That will change the signature of those methods

// from
func (ctx Context) GetString(key interface{}, defaultValue ...string) string {

// to
func (ctx Context) GetString(key interface{}, defaultValue ...string) (string, error) {

Here's an example implementation:

func (ctx Context) GetString(key interface{}, defaultValue ...string) (string, error) {
	if len(defaultValue) > 1 {
       return"", fmt.Errorf("allowed to pass only 1 default value but %d got", len(defaultValue))
    }

	if _, ok := ctx.values[key]; !ok {
		if len(defaultValue) == 1 {
			return defaultValue[0]
		}
		return "", fmt.Errorf("the key %+v does not exist", key)
	}

	value, ok := ctx.values[key].(string)
	if !ok {
		return "", fmt.Errorf("the expected value is not string (%T)", key)
	}
	return value
} 

and in a test step

stringVal, err := ctx.GetString("what-i-want")
if err != nil {
    t.Fatal(err)
}

This code would follow "handle errors explicitly" and general Go conventions but will add some boilerplate to the end user's code. Tradeoffs :)

[arberiii]

It look great to me, it would definitely help with debugging and its not that much to the end user's code as you said is Go convention so users are used to it.

[bkielbasa]

Do you have any arguments against the change? If now, I think I'll go for it.