How to log type assertion errors in golang?

Question

I have an array of some data which I want to map in []string. I can do it in 2 ways:

a)

// someData
s := someData.([]string)

In this case, the execution would stop after listing the error on the console.

b)

// someData
s, ok := someData.([]string)

In this case, no errors would occur but s will have its zero-value

---

I want to log the errors in such type assertion failure cases without stopping the execution. However, when I am using type (b), I cannot see the error details.

The only solution I can think is to use reflect.TypeOf and print both the types.

Is there any other way we can get the error when using solution (b)?

Answer 1

You can construct the log message yourself. There's no need for explicit calls to reflect as there's a printf format string %T that produces the type.

s, ok := someData.([]string)
if !ok {
    log.Printf("got data of type %T but wanted []string", someData)
    ... handle the failure somehow
}

Without knowing the context it's hard for me to produce a useful and informational log statement, but you can adapt the idea to suit your use case.