Go Strings to Bytes: When Does `[]byte(string)` Copy, and Why?

Understanding the Difference Between []byte(string) and []byte(*string)

In Go, []byte(string) is a type conversion, not a function call. This conversion allows you to transform a string into a slice of bytes. However, one significant difference between []byte(string) and []byte(*string) is that the former involves copying while the latter does not.

Why Copying is Necessary for []byte(string)

When converting a string to []byte using []byte(string), Go must perform a copy of the input argument to ensure the immutability of the original string. This is crucial because strings are immutable, meaning their content cannot be modified once created. If a byte slice were to point to the original string and allow modifications, it would violate string immutability.

Optimization Exceptions

In specific situations, Go may optimize away the copying required for []byte(string) conversion. These optimizations occur when the compiler can guarantee that the immutable string cannot be modified, ensuring memory efficiency. For example, in certain map lookups and byte iteration scenarios, the compiler may identify and remove unnecessary copying.

Benefits of Copying

The extra copying in []byte(string) offers benefits despite the potential performance hit:

• Protection against string modification: The copy ensures that any changes made to the byte slice will not affect the original string.
• Flexibility in byte slice manipulation: The copied byte slice can be mutated and modified without compromising the immutability of the original string.

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