以下摘自The Go Programming Language：
A string contains an array of bytes that, once created, is immutable. By contrast, the elements of a byte slice can be freely modified.
Strings can be converted to byte slices and back again:
s := “abc”
b := []byte(s)
s2 := string(b)Conceptually, the []byte(s) conversion allocates a new byte array holding a copy of the bytes of s, and yields a slice that references the entirety of that array. An optimizing compiler may be able to avoid the allocation and copying in some cases, but in general copying is required to ensure that the bytes of s remain unchanged even if those of b are subsequently modified. The conversion from byte slice back to string with string(b) also makes a copy, to ensure immutability of the resulting string s2.
由于Go语言中字符串是不可修改的，因此如果要修改其中内容，就要把其转化成byte slice。此外，byte slice也可以转化成字符串。这两种转化都需要分配一块新的内存，然后进行内容拷贝。