Why Does Go Differentially Treat Methods on T and *T?

Why Does Go Discriminate Method Sets on T and *T?

Understanding the distinction between methods on T (value receiver) and T (pointer receiver) is crucial in Go. Methods on T affect the copy of the variable, while methods on T manipulate the actual data.

Reason for Discrimination

The reason behind this asymmetry stems from the fact that obtaining the address of an arbitrary variable is not always feasible. While variables typically reside in memory, optimizations can make their addresses dynamic.

Consider a variable stored in a map:

<code class="go">res := TMap["key"].pointerMethod()</code>

In this example, obtaining a pointer to the variable within the map would require the runtime to ensure that memory addresses remain static. This would impose limitations on the internal implementation of the map, reducing its efficiency.

Pros and Cons of Design

Pros:

• Enforces immutability: Methods on T guarantee that the original value is not modified, preserving its integrity.
• Avoids unintended modifications: Passing a *T to a method that takes a T prevents accidental changes to the underlying data.

Cons:

• Increased complexity: It can add complexity to code when understanding the implications of using value or pointer receivers.
• Performance overhead: Dereferencing pointers introduces additional runtime overhead, especially when repeatedly accessing values from a pointer.

Conclusion

Go's discrimination between methods on T and *T is based on the challenges associated with obtaining a static address for all variables. This design preserves the immutability of values and avoids unintended modifications to data, at the cost of potential performance overhead and increased complexity.

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