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Last updated at 2023-07-25

What is the difference between Rust “String” and “str”?

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Jul 25, 2023 08:08 PM
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Jul 25, 2023
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Rust is a multi-paradigm, general-purpose programming language that emphasizes performance, type safety, and concurrency. It is designed to enforce memory safety, ensuring that all references point to valid memory, without requiring the use of a garbage collector or reference counting present in other memory-safe languages. Rust's syntax is similar to that of C and C++, although many of its features are more influenced by functional programming languages. It aims to support concurrent systems programming, which has inspired a feature set emphasizing safety, control of memory layout, and concurrency. Safety in Rust includes the guarantees of memory safety, type safety, and lack of data races[1].
In Rust, there are two types for representing strings: String and str. While both types represent strings, they differ in their ownership and mutability. Here are the differences between String and str:
  1. Ownership: String is a heap-allocated string type that owns its contents, while str is a string slice that borrows its contents from another string.
  1. Mutability: String is mutable, meaning that its contents can be changed, while str is immutable, meaning that its contents cannot be changed.
  1. Length: String has a dynamic length, meaning that its length can change at runtime, while str has a fixed length, meaning that its length is determined at compile-time.
  1. Representation: String is represented as a Vec<u8> under the hood, while str is represented as a pointer to a sequence of bytes in memory.
Here are some examples of how to use String and str in Rust:
// Creating a new String let mut s = String::new(); s.push_str("hello"); // Creating a string slice from a String let slice = &s[0..2]; // Creating a string slice from a string literal let slice = "hello world"; // Converting a String to a string slice let s = String::from("hello"); let slice = &s[..]; // Converting a string slice to a String let slice = "hello"; let s = slice.to_string();
In conclusion, String and str are both string types in Rust, but they differ in ownership, mutability, length, and representation. Understanding the differences between these types is important for writing safe and efficient Rust code. Rust's focus on memory safety and concurrency makes it a powerful language for system programming, and its ownership and borrowing mechanisms make it much easier to express common C++-style idioms and ensure they are used safely[1][5][6].
 

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