Procedural macros that take a literal integer (or the result of an evaluation of simple mathematical expressions or an environment variable whose value is a literal integer) and convert it to a typenum::Unsigned
/ typenum::Integer
typelevel positive/negative/unsigned integer.
Assuming you want a typelevel positive integer 84938493
, tnconst![+84938493]
outputs directly typenum::PInt<U84938493>
(by the way, U84938493
does not exist in typenum::consts
). The alternative is to type PInt<Sum<Prod<Exp<..., ...>, ...>, ...>, ...>
(which argubly takes a lot more time).
Example:
# use core::marker::PhantomData;
# use typenum_consts::tnconst;
# use typenum::*;
#
# #[cfg(target_pointer_width = "32")]
# type I32OrI64 = i32;
# #[cfg(target_pointer_width = "64")]
# type I32OrI64 = i64;
type ActualPositive84938493Type = tnconst![+84938493];
type ExpectedPositive84938493Type = PInt< // `PInt` implies positive integer at the type level
Sum<
Prod<Exp<U10, U7>, U8>, // 10**7 * 8
Sum<
Prod<Exp<U10, U6>, U4>, // 10**6 * 4
Sum<
Prod<Exp<U10, U5>, U9>, // 10**5 * 9
Sum<
Prod<Exp<U10, U4>, U3>, // 10**4 * 3
Sum<
Prod<Exp<U10, U3>, U8>, // 10**3 * 8
Sum<
Prod<Exp<U10, U2>, U4>, // 10**2 * 4
Sum<
Prod<Exp<U10, U1>, U9>, // 10**1 * 9
Sum<
Prod<Exp<U10, U0>, U3>, // 10**0 * 3
U0>>>>>>>>
>;
typenum::assert_type_eq!(ExpectedPositive84938493Type, ActualPositive84938493Type);
assert_eq!(
<ExpectedPositive84938493Type as typenum::ToInt<I32OrI64>>::INT,
<ActualPositive84938493Type as typenum::ToInt<I32OrI64>>::INT
);
Suppose in different environments you want a different typelevel integer, you can either use e.g. #[cfg(production)] type NUMBER = U69;
or you can do the following:
use typenum::{U69, assert_type_eq};
use typenum_consts::uconst;
// ``` .env
// ENV_VAR=69
// ```
type E = uconst![env!("ENV_VAR");];
assert_type_eq!(E, U69);
All four macros, namely, tnconst![...]
, pconst![...]
, uconst![...]
and nconst![...]
, can read literal integers from the environment.
Take pconst![...]
as the example (the rest of the macros work almost identically).
use typenum::{P123, assert_type_eq};
use typenum_consts::pconst;
type A = pconst![123];
assert_type_eq!(A, P123);
use typenum::{P15, assert_type_eq};
use typenum_consts::pconst;
type D = pconst![{
a = 10;
b = 5;
a + b; // Last statement is always the final returned value to be casted into `typenum` typelevel integer, P15
}];
assert_type_eq!(D, P15);
Note: env!(...)
is a macrolike invocation. The first parameter is mandatory and is the key of the environment variable that pconst
will read. The second parameter is optional and is the file path of the .env.*
file to read the environment variable from, e.g. env!("ENV_VAR", "./.env.prod")
, "ENV_VAR"
is the key to read the value from and "./.env.prod"
is the file path relative to CARGO_MANIFEST_DIR
.
use typenum::{P69, assert_type_eq};
use typenum_consts::pconst;
// ``` .env
// ENV_VAR=69
// ```
type E = pconst![env!("ENV_VAR");];
assert_type_eq!(E, P69);
 Feature gate evaluation of mathematical expressions and reading from environment variables.
 Enable testing for Rust version 1.70.
Licensed under either of

Apache License, Version 2.0

MIT license
at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache2.0 license, shall be dual licensed as above, without any additional terms or conditions.