substrings and the Go garbage collector

Question

When taking a substring of a string in Go, no new memory is allocated. Instead, the underlying representation of the substring contains a Data pointer that is an offset of the original string's Data pointer.

This means that if I have a large string and wish to keep track of a small substring, the garbage collector will be unable to free any of the large string until I release all references to the shorter substring.

Slices have a similar problem, but you can get around it by making a copy of the subslice using copy(). I am unaware of any similar copy operation for strings. What is the idiomatic and fastest way to make a "copy" of a substring?

Answer 1

For example,

package main

import (
    "fmt"
    "unsafe"
)

type String struct {
    str *byte
    len int
}

func main() {
    str := "abc"
    substr := string([]byte(str[1:]))
    fmt.Println(str, substr)
    fmt.Println(*(*String)(unsafe.Pointer(&str)), *(*String)(unsafe.Pointer(&substr)))
}

Output:

abc bc
{0x4c0640 3} {0xc21000c940 2}