How to Effectively Deep Copy Data Structures in Go?

How to Deep Copy Data Structures in Go

Introduction

Deep copying a data structure involves creating a new instance that contains the same data as the original but is independent from it. In Go, where there are no built-in deep copy functions, external libraries like gods may come in handy for this purpose. However, understanding the limitations of such libraries within the Go ecosystem is crucial.

Using a Third-Party Library for Deep Copy

Let's consider a scenario where we use gods to perform a deep copy of a hash set:

var c, d hashset.Set
c = *hashset.New()
c.Add(1)
deepcopy.Copy(d, c)
c.Add(2)
fmt.Println(c.Contains(2)) // true
fmt.Println(d.Contains(2)) // false
fmt.Println(c.Contains(1)) // true
fmt.Println(d.Contains(1)) // false

Contrary to our expectations, the deep copy operation doesn't fully replicate the content of the hash set. Issues arise due to the library's inability to copy unexported values.

Limitations of Deep Copying Libraries

The gods library, like many other similar libraries, faces limitations when it comes to copying unexported values due to the restrictions imposed by Go's design. This implies that fully duplicating a data structure instance with such libraries requires modifications to their code, an undesirable solution due to its complexity.

Idiomatic Approach to Deep Copying

Unfortunately, Go provides no native way to perform deep copying. Reflection, a tool that allows for reading unexported fields, cannot be used to set them. Using the unsafe package, though possible, is discouraged due to its potential for creating unstable and platform-dependent programs.

The lack of an idiomatic deep copy approach emphasizes the importance of supporting cloning within the package itself.

Alternative "Cloning" Techniques

While Go lacks dedicated deep copy mechanisms, certain workarounds exist in specific scenarios. For instance, maps can be cloned by creating a new map and manually iterating over key-value pairs for duplication.

Another technique is using assignment to create "exact" copies of structs, including unexported fields. However, this approach does not allow for altering unexported fields in the copied instance.

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