String based on generic array
Since rust doesn't have constant generics yet typenum is used to allow for generic arrays (U1 to U255)
If you need bigger than U255 open an issue explaining your use-case and we may implement
Can't outgrow initial capacity (defined at compile time), always occupies capacity + 1 bytes of memory
Doesn't allocate memory on the heap and never panics in release (all panic branches are stripped at compile time - except Index/IndexMut traits, since they are supposed to)
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.
default: std
std enabled by default, enables std compatibility - impl Error trait for errors (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
diesel-traits enables diesel traits integration (Insertable/Queryable)
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
```rust use arraystring::{Error, ArrayString, typenum::U5, typenum::U20};
type Username = ArrayString
pub struct User { pub username: Username, pub role: Role, }
fn main() -> Result<(), Error> { let user = User { username: Username::tryfromstr("user")?, role: Role::tryfromstr("admin")? }; println!("{:?}", user);
Ok(())
} ```
## Benchmarks
This benchmarks ran while I streamed video and used my computer (with non-disclosed specs) as usual, so don't take the actual times too serious, just focus on the comparison
```mycustombenchmark string clone 25.850 ns
small-string (21 bytes) clone 4.556 ns small-string (21 bytes) tryfromstr 15.749 ns small-string (21 bytes) fromstrtruncate 10.991 ns
cache-string (63 bytes) clone 10.345 ns cache-string (63 bytes) tryfromstr 24.959 ns cache-string (63 bytes) fromstrtruncate 17.485 ns
max-string (255 bytes) clone 145.750 ns max-string (255 bytes) tryfromstr 157.890 ns max-string (255 bytes) fromstrtruncate 193.870 ns max-string (255 bytes) fromstrunchecked 163.740 ns ```
MIT and Apache-2.0