What's the Difference Between `[]byte(string)` and `[]byte(*string)` in Go?

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

In Go, the []byte(string) expression is not a method call but a type conversion from a string to a byte slice. This conversion involves creating a copy of the input string because the resulting byte slice is mutable, while the original string is immutable.

Immutability of Strings

According to the Go language specification, strings are immutable, meaning their content cannot be modified once created. This restriction ensures data integrity and prevents potential synchronization issues.

Implications for []byte(string) Conversion

When converting a string to a byte slice using []byte(string), a copy must be made to maintain the immutability of the original string. This copy ensures that any modifications made to the byte slice do not affect the original string value.

Optimized Cases

However, in some specific situations, the copying process is optimized away by the Go compiler. These optimizations occur when it can prove that the resulting byte slice will not alter the original string.

One example is when indexing a map using a byte slice converted from a string. In this case, the compiler recognizes that the string's mutability is not violated because map keys are effectively immutable.

Another optimization occurs when ranging over the bytes of a string that has been converted to a byte slice. The compiler recognizes that the original string's content will not be modified since the loop operates on the byte slice.

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