Macro fixed_alias 

macro_rules! fixed_alias {
    ($vis:vis $name:ident, $size:literal, $doc:literal) => { ... };
    ($vis:vis $name:ident, $size:literal) => { ... };
    ($name:ident, $size:literal, $doc:literal) => { ... };
    ($name:ident, $size:literal) => { ... };
}

Creates a type alias for Fixed<[u8; N]>.

Generates a named, optionally-documented type alias with a compile-time zero-size guard. The generated type inherits all Fixed<[u8; N]> methods including expose_secret(), with_secret(), to_hex(), etc.

Syntax

fixed_alias!(pub Name, N);                // public, auto-generated doc
fixed_alias!(pub(crate) Name, N);         // crate-visible
fixed_alias!(Name, N);                    // private
fixed_alias!(pub Name, N, "doc string");  // with custom doc

Examples

All three visibility forms:

use secure_gate::{fixed_alias, RevealSecret};

fixed_alias!(pub Aes256Key, 32);           // public
fixed_alias!(pub(crate) HmacKey, 32);      // crate-visible
fixed_alias!(private_nonce, 12);           // private (no modifier)

let key: Aes256Key = [42u8; 32].into();
key.with_secret(|b| assert_eq!(b.len(), 32));

With a custom doc string:

use secure_gate::{fixed_alias, RevealSecret};

fixed_alias!(pub ApiKey, 32, "32-byte API authentication key.");
let key: ApiKey = [0u8; 32].into();
assert_eq!(key.expose_secret(), &[0u8; 32]);

Zero-size is a compile error (caught by the zero-size guard):

use secure_gate::fixed_alias;
fixed_alias!(pub Bad, 0); // compile-time error: index out of bounds

Implementation Notes

Each expansion emits const _: () = { let _ = [(); N][0]; }; — a zero-cost compile-time guard that rejects N = 0 with a const-evaluation panic. This is the only size check performed at compile time; there are no runtime checks for other size constraints. Validate expected sizes in unit tests:

use secure_gate::{fixed_alias, RevealSecret};

fixed_alias!(pub ChaChaKey, 32);
// In your tests:
assert_eq!(core::mem::size_of::<ChaChaKey>(), 32);