使用反射调用带有nil参数的函数会导致“使用零值参数调用”的紧急情况

Question

I'm trying to test a function that accepts a parameter of the type "error". The function should panic under certain situations and I'm trying to test scenarios.

However, when I try to use reflect.Call on a nil value (which can be passed into a function that accepts something of type "error"), it seems to result in a panic with the following message:

reflect: Call using zero Value argument

I have found the following posts but I am failing to integrate it into my function.

• https://groups.google.com/forum/#!topic/golang-nuts/apNcACpl_fI
• https://groups.google.com/forum/#!topic/golang-nuts/WOUft8EZQ1I

Relevant Go Playground: http://play.golang.org/p/cYQMQ6amPH

In the playground above, I would like the call to InvocationCausedPanic(PanicOnErr, nil) to return false, however, the above panic from reflect is causing a false positive.

Are there any modifications I can make to the InvocationCausedPanic or the invoke functions to make this work (while retaining its ability to test other functions that cannot accept nil as an argument - a function that accepts a string for instance)?

Perhaps the issue is in how the function is called?

I've tred things like InvocationCausedPanic(PanicOnErr, new(error)) or InvocationCausedPanic(PanicOnErr, error(nil)) to no avail.

Thanks for any advice.

Answer 1

If the parameter value is nil, then use a zero value of the function parameter type.

    if paramValue == nil {
        reflectedParams[paramIndex] = reflect.New(expectedType).Elem()
    } else {
        reflectedParams[paramIndex] = reflect.ValueOf(paramValue)
    }

<kbd>playground</kbd>

You can simplify the code if you compute the reflect value and then check assignability. With this change, the compatible function is not required.

for paramIndex, paramValue := range params {
    if paramValue == nil {
        reflectedParams[paramIndex] = reflect.New(expectedType).Elem()
    } else {
        reflectedParams[paramIndex] = reflect.ValueOf(paramValue)
    }
    expectedType := funcType.In(paramIndex)
    actualType := reflectedParams[paramIndex].Type()
    if !actualType.AssignableTo(expectedType) {
        errStr := fmt.Sprintf("InvocationCausedPanic called with a mismatched parameter type [parameter #%v: expected %v; got %v].", paramIndex, expectedType,actualType)
        panic(errStr)
    }
}