What are the differences between Rust's `String` and `str`?

Question

Why does Rust have String and str? What are the differences between String and str? When does one use String

Answer 1

I have a C++ background and I found it very useful to think about String and &str in C++ terms:

• A Rust String is like a std::string; it owns the memory and does the dirty job of managing memory.
• A Rust &str is like a char* (but a little more sophisticated); it points us to the beginning of a chunk in the same way you can get a pointer to the contents of std::string.

Are either of them going to disappear? I do not think so. They serve two purposes:

String keeps the buffer and is very practical to use. &str is lightweight and should be used to "look" into strings. You can search, split, parse, and even replace chunks without needing to allocate new memory.

&str can look inside of a String as it can point to some string literal. The following code needs to copy the literal string into the String managed memory:

let a: String = "hello rust".into();

The following code lets you use the literal itself without copy (read only though)

let a: &str = "hello rust";