ArrayString

Generic-array based string

Since rust doesn't have constant generics yet typenum is used to allow for generic arrays (through generic-array crate)

Can't outgrow capacity (defined at compile time), always occupies capacity + 1 bytes of memory

Doesn't allocate memory on the heap and never panics (all panic branches are stripped at compile time)

• Documentation

Why

Data is generally bounded, you don't want a phone number with 30 characters, nor a username with 100. You probably don't even support it in your database.

Why pay the cost of heap allocations of strings with unlimited capacity if you have limited boundaries?

Stack based strings are generally faster to create, clone and append to than heap based strings (custom allocators and thread-locals may help with heap based ones).

But that becomes less true as you increase the array size, CacheString occuppies a full cache line, 255 bytes is the maximum we accept - MaxString (bigger will just wrap) and it's probably already slower than heap based strings of that size (like in std::string::String)

There are other stack based strings out there, they generally can have "unlimited" capacity (heap allocate), but the stack based size is defined by the library implementor, we go through a different route by implementing a string based in a generic array.

Array based strings always occupies the full space in memory, so they may use more memory (in the stack) than dynamic strings.

TODO: bench against other implementations

Features

default: std

• std enabled by default, enables std compatibility (remove it to be #[no_std] compatible)

• serde-traits enables serde traits integration (Serialize/Deserialize)

  Opperates like String, but truncates it if it's bigger than capacity

• logs enables internal logging

  You will probably only need this if you are debugging this library

Examples

use arraystring::{Error, ArrayString, typenum::U5, typenum::U20};

type Username = ArrayString<U20>;
type Role = ArrayString<U5>;

#[derive(Debug)]
pub struct User {
    pub username: Username,
    pub role: Role,
}

fn main() -> Result<(), Error> {
    let user = User {
        username: Username::try_from_str("user")?,
        role: Role::try_from_str("admin")?
    };
    println!("{:?}", user);

    Ok(())
}

Licenses

MIT and Apache-2.0