Pointers or Values in Go Structs: When Does Performance Matter?

Pointers vs. Values in Go Structs: A Performance Perspective

In Go, structs are value types, meaning that when a struct is assigned or passed as an argument, a copy of the struct is created. However, pointers can also be used in structs to reference values, rather than copying them.

Performance Considerations

From a performance perspective, there is generally an overhead associated with using pointers in structs compared to using values. Primitive numeric types, such as integers and floats, are typically faster to copy than dereferencing a pointer. For complex data structures, the performance difference depends on the size of the structure. If the structure is smaller than a cache line (typically around 128 bytes), copying may still be faster.

For larger structures, benchmarking is recommended to determine the optimal approach. Factors such as data locality and cache friendliness can significantly impact performance.

When to Use Pointers

Choosing between pointers and values in structs should be based primarily on the logical requirements of the program. Pointers should be used when:

• Modification is Required: If the value needs to be modified from multiple places in the program, using a pointer allows for direct modification of the referenced value.
• Nil Handling: Pointers allow for the possibility of a nil value, indicating the absence of a value.
• Method Receivers: If a custom type has methods that require a pointer receiver, the struct field should use a pointer.

Alternatives to Pointers

In some cases, alternatives to pointers can provide equivalent functionality without the performance overhead. For instance, if a struct needs to be modified but nil values are not required, a composition approach can be used:

type ExpWithPointer struct {
  foo int
  bar *int
}

type ExpWithComposition struct {
  foo int
  Bar struct {
    value int
    isPresent bool
  }
}

With this approach, ExpWithComposition has a struct field Bar that includes a boolean flag to indicate the presence of the value.

Conclusion

The choice between pointers and values in Go structs should not be based solely on performance considerations. Logical requirements and design choices play a crucial role. By understanding the performance trade-offs and the appropriate use cases for pointers, developers can optimize the performance and maintainability of their Go programs.

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