Struct StrConstrue

pub struct StrConstrue<const N: usize>(/* private fields */);

Alternative to String for const

This is just a Construe<u8, N> with a few additional methods, see the Construe documentation for a little more info.

use construe::{StrConstrue, construe};

const fn hello_world<const N: usize>() -> StrConstrue<N> {
    let strc = StrConstrue::new();
    strc.push_str("Hello")
        .push_str(" ")
        .push_str("World")
        .push_str("!")
}

construe!(const HELLO_WORLD: &str = hello_world());

// or manually:
const HELLO_WORLD_2: &str = {
    const LEN: usize = hello_world().needs_len();
    const ARRAY: [u8; LEN] = hello_world().store_bytes();
    StrConstrue::borrow_str(&ARRAY)
};

assert_eq!(HELLO_WORLD, "Hello World!");
assert_eq!(HELLO_WORLD, HELLO_WORLD_2);

Implementations

impl<const N: usize> StrConstrue<N>

pub const fn new() -> Self

Create a StrConstrue instance (with or without the buffer)

pub const fn len(&self) -> usize

Amount of bytes stored (or supposed to be stored) in the buffer

pub const fn is_empty(&self) -> bool

Whether there are no bytes (supposed to be) stored in the buffer

pub const fn push_str(self, s: &str) -> Self

Push a &str into the buffer

Note that this takes self by-value: since &mut references aren’t yet stable in const contexts, we have to keep reassigning the output of the function to the variable.

// `mut` because we reassign to it
let mut sc = construe::StrConstrue::<0>::new();
sc = sc.push_str("Test");
// method chaining can save space
sc = sc.push_str("123").push_str(" ").push_str(":^)");

pub const fn store_bytes(self) -> [u8; N]

Return the assembled byte buffer, consuming the struct

Panics if the buffer is not filled or if this is a zero-length buffer that was supposed to store bytes.

Use StrConstrue::borrow_str to obtain a &str from the buffer.

impl StrConstrue<0>

pub const fn needs_len(&self) -> usize

Amount of bytes needed to store the string

This is the same as StrConstrue::len, but it exists as a separate method that’s only implemented for N = 0 so that the const N: usize generic parameter on functions returning this can be inferred as 0 for the first run.

pub const fn borrow_str(byte_slice: &[u8]) -> &str

Borrow a &str from a byte slice

See the example at the top for how to use this, the buffer returned by StrConstrue::store_bytes needs to be stored in a constant to be able to borrow a &'static str from it.

This just calls core::str::from_utf8 and panics if the byte slice contains invalid UTF-8.