Why Does Go Separate String Functions into a `strings` Package Instead of Defining Methods Directly on the `string` Type?

Method Definition on Basic Types in Go: A Design Choice

One commonly raised inquiry in the Go community revolves around the rationale behind defining string functions in a separate package, as opposed to directly on the string data type. This design decision has sparked discussions regarding custom string types and the accessibility of builtin functions.

Why not Define Methods on String Type Directly?

The primary reason for defining string functions in the strings package is to preserve the simplicity of the language. Go's design disallows method definition on basic types defined outside of the language itself. Since string is one such type, adding methods to it would require significant language/compiler modifications.

Custom String Types and Method Accessibility

The concern that custom string types cannot access builtin functions is unfounded. While custom string types can extend string, they cannot define methods that override the builtins. This is because the language design only permits methods on types within the same package.

Supporting Evidence from Go Creators

This design decision is further solidified by statements from Go creator Rob Pike:

• "Go does not have methods on basic types... partly because of the knock-on effect they might have on interfaces."
• "Making all [string functions] methods on the basic type would complicate the language."

Benefits of Library-Based String Functions

In addition to language simplicity, the strings package offers several advantages:

• Maintainability: Functions are easier to isolate and update in a dedicated package.
• Extensibility: Additional string functions can be seamlessly added without modifying the string type itself.
• Flexibility: The library approach allows string functions to be applied to a variety of types that implement the Stringer interface, providing a consistent interface for custom data structures.

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