Can Go\'s Reflection Package Enable Generic Element Presence Checks in Slices?

Can Generic Code be Implemented to Determine Element Presence in Go Slices?

In Go, determining whether a slice contains a specific element is a common operation. However, for every new slice type, implementing this logic can seem tedious.

One attempted solution involves using an interface{} slice, as seen in the code snippet:

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

However, this approach is hindered by the nature of interface{} and the requirement to implement it for each new slice type.

Fortunately, Go's reflection package provides a generic solution:

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

    sv := reflect.ValueOf(slice)

    // Check slice type.
    if sv.Kind() != reflect.Slice && sv.Kind() != reflect.Array {
        return false
    }

    // Iterate slice and compare elements.
    for i := 0; i < sv.Len(); i++ {
        if elem == sv.Index(i).Interface() {
            return true
        }
    }

    // Element not found.
    return false
}</code>

This function takes two parameters: the slice and the element to find. It uses reflection to determine if the slice is a slice or an array, then iterates over its elements using the ValueOf() and Index() methods.

While this generic approach is convenient, it comes at the cost of performance. Benchmarks show that it can be 50-60 times slower than non-generic versions, as seen below:

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

Benchmark Results:

• Generic: N=100000, 73.023214ms, 730.23214 ns/op
• Non-Generic: N=100000, 1.315262ms, 13.15262 ns/op

Therefore, while the generic Contains() function provides versatility, it should be used judiciously to avoid performance bottlenecks.

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