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🧵 Strings

👀 Fast Lookup

  • &str: Hardcoded string literal, immutable, and not heap-allocated.
  • String: Heap-allocated, mutable, and can grow in size.
  • Use &str for static strings and String for dynamic strings.
  • Use chars() for most character operations, but be aware of performance implications.

🏷️ Types of Strings in Rust

  • &str: Core string type, borrowed, immutable, and not heap-allocated.
  • String: Owned string type, defined in the standard library, mutable, heap-allocated, and can grow in size. It is a wrapper around a Vec<u8> that guarantees valid UTF-8.
  • ...

🤔 When to use &str vs String

  • Use &str when you
    • You're writing a function that only needs to read a string, not change it. This is more flexible because you can pass both a String and a &str to it!
    • You want to pass a string literal.
  • Use String when you
    • Need to create or modify string data at runtime.
    • Need a function to return a string that it creates.
    • Need to store a string in a struct that should own its data.

🔧 Working with Strings

Rust's String and &str types are UTF-8 encoded, which means a single character can take up to 4 bytes. This means calling len() will not guarantee the number of characters. Also, indexing into a String or &str with a number will panic if the index is not valid. Then how do you get the number of characters in a string and access characters safely?

  • Use the chars() method to iterate over characters in a string.
    • chars().count() returns the number of characters in a string.
    • Use for c in text.chars() to iterate over characters.
    • chars().nth(n) returns the Option<char> at index n, which is safe.

However, chars() is not fast. It has O(n) complexity because it has to iterate through the string to count characters.

My conclusion is that use chars() as default for character related operations. However, if we are dealing with a lot of characters and performance is critical, use slicing &str[start..end] to get a substring, which is O(1) because it just creates a new &str that points to the same data without copying.