A string slice is a reference to part of a String. It is created using a range within brackets, where the starting index is the first position in the slice and the ending index is one more than the last position in the slice. For example, the following code creates a string slice called `hello` that refers to the first 5 characters of the string `s`:
let s = String::from("hello world");
let hello = &s[0..5];
String slices can be used to access a portion of a string without having to copy the entire string. This can be useful for performance reasons, as well as for avoiding memory leaks. Here is an example of how to use a string slice to access a portion of a string:
let s = String::from("hello world");
let hello = &s[0..5];
println!("{}", hello); // prints "hello"
As you can see, the `hello` string slice refers to the first 5 characters of the `s` string. When we print the `hello` string slice, the Rust compiler will only print the first 5 characters of the `s` string.
String slices are a powerful tool that can be used to access and manipulate portions of strings. They can be used to improve performance and avoid memory leaks.
String Literals as Slices
In Rust, a string literal is a slice that points to a constant string of bytes in the binary. The type of a string literal is &str, which is a reference to a string slice. This means that string literals are immutable, because they are just references to a constant piece of data. For example, the following code:
let s = "Hello, world!";
creates a string literal with the value "Hello, world!". The type of `s` is `&str`, which is a reference to a string slice. This means that `s` is a pointer to the constant string of bytes that make up the string literal "Hello, world!".
String literals are stored in the read-only data section of the binary, which means that they cannot be modified. This is why string literals are immutable. Here is an example of how to use a string literal as a slice:
let s = "Hello, world!";
let first_word = &s[0..5];
assert_eq!(first_word, "Hello");
This code first creates a string literal with the value "Hello, world!". Then, it creates a slice that starts at the beginning of the string literal and ends at the fifth character. The slice is then assigned to the variable `first_word`. Finally, the code asserts that the value of `first_word` is equal to "Hello".
String Slices as Parameters
String slices are references to a contiguous sequence of elements in a string. They can be used as parameters to functions, which allows us to be more flexible in the way we pass strings to functions. For example, the following function takes a string slice as a parameter:
fn first_word(s: &str) -> &str {
let mut end = 0;
for (i, c) in s.chars().enumerate() {
if c == ' ' {
return &s[0..end];
}
end = i + 1;
}
return &s[..];
}
This function can be used to find the first word in a string. We can pass a string slice to this function, or we can pass a reference to a String. For example:
let my_string = String::from("hello world");
let word = first_word(&my_string);
In this example, we are passing a reference to the `String` `my_string` to the `first_word` function. The `first_word` function will then treat the `String` as a string slice and find the first word in it.
