Software Development

Converting Rust String To And From

Rust &str and String is different in a sense that str is static, owned and fix sized while String can be dynamically allocated once and be converted to mutable to be appended. Most of the time you’ll be working with String on Rust when re-allocating and moving values between structs.

There are times you may need to convert dynamic string to char bytes and static string. Here are ways to do it:

From &str

  • &str -> String has many equally valid methods: String::from(st), st.to_string(), st.to_owned().
    • But I suggest you stick with one of them within a single project. The major advantage of String::from is that you can use it as an argument to a map method. So instead of|s| String::from(s)) you can often use
  • &str -> &[u8] is done by st.as_bytes()
  • &str -> Vec<u8> is a combination of &str -> &[u8] -> Vec<u8>, i.e. st.as_bytes().to_vec() or st.as_bytes().to_owned()

From String

  • String -> &str should just be &s where coercion is available or s.as_str() where it is not.
  • String -> &[u8] is the same as &str -> &[u8]: s.as_bytes()
  • String -> Vec<u8> has a custom method: s.into_bytes()

From &[u8]

  • &[u8] -> Vec<u8> is done by u.to_owned() or u.to_vec(). They do the same thing, but to_vec has the slight advantage of being unambiguous about the type it returns.
  • &[u8] -> &str doesn’t actually exist, that would be &[u8] -> Result<&str, Error>, provided via str::from_utf8(u)
  • &[u8] -> String is the combination of &[u8] -> Result<&str, Error> -> Result<String, Error>

From Vec<u8>

  • Vec<u8> -> &[u8] should be just &v where coercion is available, or as_slice where it’s not.
  • Vec<u8> -> &str is the same as Vec<u8> -> &[u8] -> Result<&str, Error> i.e. str::from_utf8(&v)
  • Vec<u8> -> String doesn’t actually exist, that would be Vec<u8> -> Result<String, Error> via String::from_utf8(v)

Coercion is available whenever the target is not generic but explicitly typed as &str or &[u8], respectively. The Rustonomicon has a chapter on coercions with more details about coercion sites.


&str    -> String  | String::from(s) or s.to_string() or s.to_owned()
&str    -> &[u8]   | s.as_bytes()
&str    -> Vec<u8> | s.as_bytes().to_vec() or s.as_bytes().to_owned()
String  -> &str    | &s if possible* else s.as_str()
String  -> &[u8]   | s.as_bytes()
String  -> Vec<u8> | s.into_bytes()
&[u8]   -> &str    | s.to_vec() or s.to_owned()
&[u8]   -> String  | std::str::from_utf8(s).unwrap(), but don't**
&[u8]   -> Vec<u8> | String::from_utf8(s).unwrap(), but don't**
Vec<u8> -> &str    | &s if possible* else s.as_slice()
Vec<u8> -> String  | std::str::from_utf8(&s).unwrap(), but don't**
Vec<u8> -> &[u8]   | String::from_utf8(s).unwrap(), but don't**

* target should have explicit type (i.e., checker can't infer that)

** handle the error properly instead

By Edward Fitz Abucay

"How long is forever?"

I'm a software engineer with a passion for innovating and creating products, especially for startups in the web3 and blockchain space. I'm always excited to learn and work with new technologies, and I'm committed to delivering high-quality solutions that meet the needs of my clients or users.

In my free time, I enjoy listening to music of all genres, but classical music holds a special place in my heart. I find it both inspiring and calming, and it helps me to stay focused and creative. I'm also an avid reader of books and manga, and I enjoy discovering new authors and stories.

As a software engineer, I have a strong technical background with experience in various programming languages, frameworks, and tools. I'm always striving to improve my skills and stay up-to-date with the latest trends and best practices. I love working with startups, especially those in the web3 and blockchain space, because I believe that these technologies have the potential to revolutionize the way we live and work.

Overall, I'm a dedicated and driven individual with a wide range of interests and skills. I believe that my passion for software engineering, combined with my love of music and reading, makes me a well-rounded and adaptable professional.

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