Embedding in Go: Pointer vs. Value: When Should You Use Each?

Embedding in Go: Pointer vs. Value

Embedding is a powerful technique in Go that allows you to reuse code and share functionality between types. When embedding, you can decide whether to embed a type by pointer or by value. This article explores the differences between these two approaches and provides guidance on which one is preferable.

Embedding by Pointer

Embedding by pointer involves creating a field in the embedding type that points to the embedded type. This allows for greater control over the embedded type, as you can access its pointer methods directly. For example:

type Bitmap struct {
    data [4][4]bool
}

type Renderer struct {
    *Bitmap
    on uint8
    off uint8
}

Embedding by Value

Embedding by value, on the other hand, copies the embedded type into the embedding type. This approach results in a smaller memory footprint and eliminates the need to dereference pointers. For instance:

type Bitmap struct {
    data [4][4]bool
}

type Renderer struct {
    Bitmap  // Embed by value
    on uint8
    off uint8
}

Which Approach to Use?

The choice between embedding by pointer or by value depends on the specific use case. Consider the following factors:

1. Method Access: If the embedded type has pointer methods that you need to access, then you must embed by pointer.
2. By-Value Copying: If the embedded type is passed around by value, embedding by pointer avoids unnecessary memory copying.
3. Constructor Return Type: If the embedded type has a constructor that returns a pointer and the zero value of the embedded type is unusable, then embed by pointer to prevent accidental copies.
4. Method Type: If all the methods of the embedded type are value methods, then embedding by value is preferred for locality of access and reduced memory allocation.

Conclusion

Ultimately, the decision between embedding by pointer or by value is context-dependent. Understanding the differences between these approaches will help you make informed choices that optimize the performance and usability of your code.

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