How Can String Variables in Go Appear Mutable While String Values Remain Immutable?

Immutable String Values in Go

The Go specification states that strings are immutable, meaning once created, a string's contents cannot be altered. However, the following example appears to contradict this principle:

str := "hello"
fmt.Printf("%p\n",&str) // 0x1040c128
fmt.Printf("%v\n",str) // hello
ptr := &str
*ptr = "world"
fmt.Printf("%p\n",&str) // 0x1040c128
fmt.Printf("%v\n",str) // world

Here, the address of the str variable remains the same even after modifying the string value. So why is this not considered a violation of immutability?

The key distinction here is between string values and string variables. In Go, string values are immutable, but string variables are mutable. The str variable is a pointer to a string value, and changing the value of *ptr simply assigns a new value to this pointer.

To understand this, consider the following analogy:

Imagine a library book and a library card. The library book represents the string value, and the library card represents the string variable. You can check out multiple books with the same library card, just like you can assign multiple strings to the same string variable. However, once a book is checked out, its contents cannot be altered. Similarly, once a string value is created, its contents cannot be changed.

Immutability in Go ensures that string values are always consistent and reliable. Even if multiple variables refer to the same string value, any changes made to one variable will not affect the others. This is a crucial feature for ensuring data integrity and security in concurrent and distributed systems.

While immutability prevents direct modification of string values, there are techniques, such as using the unsafe package, to bypass these restrictions. However, such practices come with significant risks and are generally not recommended. Adhering to the principles of string immutability is essential for writing correct and robust Go programs.

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