# FStr: a stack-allocated fixed-length string type
[](https://crates.io/crates/fstr)
[](https://github.com/LiosK/fstr-rs/blob/main/LICENSE)
This crate provides a thin wrapper for `[u8; N]` to handle a stack-allocated byte array as a
fixed-length, `String`-like type through common traits such as `Display`, `PartialEq`, and
`Deref<Target = str>`.
```rust
use fstr::FStr;
let x = FStr::try_from(b"foo")?;
println!("{}", x); // "foo"
assert_eq!(x, "foo");
assert_eq!(&x[..], "foo");
assert_eq!(&x as &str, "foo");
assert!(!x.is_empty());
assert!(x.is_ascii());
let mut y = FStr::try_from(b"bar")?;
assert_eq!(y, "bar");
y.make_ascii_uppercase();
assert_eq!(y, "BAR");
const K: FStr<8> = FStr::from_str_unwrap("constant");
assert_eq!(K, "constant");
```
Unlike `String` and [`arrayvec::ArrayString`], this type has the same binary representation
as the underlying `[u8; N]` and manages fixed-length strings only. The type parameter takes the
exact length (in bytes) of a concrete type, and the concrete type only holds the string values
of that size.
[`arrayvec::ArrayString`]: https://docs.rs/arrayvec/latest/arrayvec/struct.ArrayString.html
```rust
let s = "Lorem Ipsum ✨";
assert_eq!(s.len(), 15);
assert!(s.parse::<FStr<15>>().is_ok()); // just right
assert!(s.parse::<FStr<10>>().is_err()); // too small
assert!(s.parse::<FStr<20>>().is_err()); // too large
```
```rust
let x: FStr<10> = FStr::from_str_unwrap("helloworld");
let y: FStr<12> = FStr::from_str_unwrap("helloworld ");
// This code does not compile because `FStr` of different lengths cannot mix.
if x != y {
unreachable!();
}
```
Variable-length string operations are partially supported by utilizing a C-style NUL-terminated
buffer and some helper methods.
```rust
let mut buffer = FStr::<20>::from_str_lossy("haste", b'\0');
assert_eq!(buffer, "haste\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0");
let c_str = buffer.slice_to_terminator('\0');
assert_eq!(c_str, "haste");
use core::fmt::Write as _;
write!(buffer.writer_at(c_str.len()), " makes waste")?;
assert_eq!(buffer.slice_to_terminator('\0'), "haste makes waste");
```
## Crate features
- `std` (optional; enabled by default) enables the integration with `std`. Disable default
features to operate this crate under `no_std` environments.
- `serde` (optional) enables the serialization and deserialization of `FStr`through `serde`.
## License
Licensed under the Apache License, Version 2.0.
## See also
- [docs.rs/fstr](https://docs.rs/fstr)