How Can I Compare `interface{}` Values for Equality in Go, Especially with Custom Structs?

Equality Checking for Interface{}

In Go, comparing interface{} values can be a bit tricky, especially when dealing with custom structs. This article aims to shed light on this aspect and provide a concise and comprehensive answer to the following question:

How do I effectively check for equality of interface{} values, particularly in cases involving user-defined structs?

Interface{} Equality

Firstly, it's essential to understand that interface{} values support equality comparison. Two interface{} values are equal if they have identical dynamic types and equal dynamic values, or if both have a nil value.

Structs and Interfaces

When comparing a struct value to an interface{} value, equality holds true only if values of the struct's type are comparable and the struct implements the interface. Furthermore, the struct's dynamic type must match the interface's dynamic type, and its dynamic value must be equal to the interface's dynamic value.

Example

Let's consider an example to illustrate this behavior:

type MyStruct struct {
    Name string
    Age  int
}

var v interface{} = MyStruct{Name: "John", Age: 30}
var A = []interface{}{MyStruct{Name: "Alice", Age: 25}, MyStruct{Name: "Bob", Age: 35}}

for i := 0; i < len(A); i++ {
    if A[i] == v {
        fmt.Println("Found")
        break
    }
}

In this scenario, the equality check between A[i] and v will succeed because both values are of type MyStruct with identical fields.

Conclusion

Equality checking in Go becomes manageable once you grasp the concepts of interface{} equality and the relationship between structs and interfaces. By understanding these principles, you can effectively compare interface{} values, including custom structs, with confidence.

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