How do you check for element presence in slices of different types in Go?

How to Generically Check for Element Presence in a Slice in Go

In Go, determining whether a slice contains a specific element can be a common scenario. However, there is no built-in method to perform this generic check across different slice types.

Failed Attempt with Interface{}

An attempt to use the interface{} type as a generic solution, as shown below, may seem plausible:

<code class="go">func sliceContains(slice []interface{}, elem interface{}) bool {
    for _, item := range slice {
       if item == elem {
          return true
       }
    }
    return false
}</code>

However, comparing values of different types (interface{}) can lead to incorrect results.

Generic Solution with Reflection

To achieve a truly generic solution, reflection can be employed. The following function uses reflection to iterate over the slice and compare each element to the target element:

<code class="go">func Contains(slice, elem interface{}) bool {

    sv := reflect.ValueOf(slice)

    // Check that slice is actually a slice/array.
    if sv.Kind() != reflect.Slice && sv.Kind() != reflect.Array {
        return false
    }

    // Iterate the slice
    for i := 0; i < sv.Len(); i++ {

        // Compare elem to the current slice element
        if elem == sv.Index(i).Interface() {
            return true
        }
    }

    // Nothing found
    return false
}</code>

This solution allows you to perform generic element checks on slices of any type.

Performance Considerations

While the generic Contains function provides the desired functionality, it comes at a significant performance cost. Benchmarking against a non-generic equivalent function yields a slowdown factor of approximately 50x. Therefore, it is crucial to evaluate the performance implications before using reflection for generic element checks.

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