Fixed capacity stack based generic string
Since rust doesn't have constant generics yet typenum is used to allow for generic arrays (U1 to U255)
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(())
} ```
## Comparisons
These benchmarks ran while I streamed video and used my computer (with non-disclosed specs) as usual, so don't take the actual times too seriously, just focus on the comparison
```mycustombenchmark small-string (23 bytes) clone 4.837 ns small-string (23 bytes) tryfromstr 14.777 ns small-string (23 bytes) fromstrtruncate 11.360 ns small-string (23 bytes) fromstrunchecked 11.291 ns small-string (23 bytes) trypushstr 1.162 ns small-string (23 bytes) push_str 3.490 ns
cache-string (63 bytes) clone 10.170 ns cache-string (63 bytes) tryfromstr 25.579 ns cache-string (63 bytes) fromstrtruncate 16.977 ns cache-string (63 bytes) fromstrunchecked 17.201 ns cache-string (63 bytes) trypushstr 1.160 ns cache-string (63 bytes) push_str 3.486 ns
max-string (255 bytes) clone 147.410 ns max-string (255 bytes) tryfromstr 157.340 ns max-string (255 bytes) fromstrtruncate 158.000 ns max-string (255 bytes) fromstrunchecked 158.420 ns max-string (255 bytes) trypushstr 1.167 ns max-string (255 bytes) push_str 4.337 ns
string (19 bytes) clone 33.295 ns string (19 bytes) from 32.512 ns
inlinable-string (30 bytes) clone 16.751 ns inlinable-string (30 bytes) from_str 29.310 ns
smallstring crate (20 bytes) clone 60.988 ns smallstring crate (20 bytes) from_str 50.233 ns ```
MIT and Apache-2.0