Build typenum from integer literal

[jerry73204]

Since only types up to 1024 and power of 2 are available in consts mod, rather than Sum<X, Y> combination, I'm wondering a convenient way to build types for large numbers.

Suppose we could have a macro like tyint!(9999999) or tyuint!(99999999)? The Rust language already has function-like procedural macros. We can make it possible by decomposing numbers into powers of 2, and turn it in into combinations of Sum<X, Y>.

Besides, I see const generics does the same job. There's still open issue that it panics the compiler.

[paholg]

I am unlikely to build it, but I would be happy with such a PR if someone else wants to.

FWIW, you can do it a bit more conveniently than using Sum<X, Y> by using the op! macro.

Ex:

type U9999999 = op!(U9 * (pow(U10, U6) + pow(U10, U5) + pow(U10, U4) + pow(U10, U3) + pow(U10, U2) + pow(U10, U1) + pow(U10, U0));

[jerry73204]

I wrote a little demo to show this idea. It works only if #![feature(proc_macro_hygiene)] unstable feature is present. That's because procedural macro is not to allowed at type positions for now (rust-lang/rust#54727). Fortunately, the feature is on the track of stabilization (rust-lang/rust#54727). We can keep it on hold, or make it an optional feature.

You can put this demo usage of tyint!() macro in tests.

#![feature(proc_macro_hygiene)]
extern crate typenum;

type U99999999999999 = typenum::tyint!(99999999999999usize);
type P99999999999999 = typenum::tyint!(99999999999999isize);

By running cargo expand --test TEST_NAME, you can see the expansion.

#![feature(prelude_import)]
#![no_std]
#![feature(proc_macro_hygiene)]
#[prelude_import]
use ::std::prelude::v1::*;
#[macro_use]
extern crate std;
extern crate typenum;
type U99999999999999 = typenum :: Sum < typenum :: consts :: U70368744177664 , typenum :: Sum < typenum :: consts :: U17592186044416 , typenum :: Sum < typenum :: consts :: U8796093022208 , typenum :: Sum < typenum :: consts :: U2199023255552 , typenum :: Sum < typenum :: consts :: U549755813888 , typenum :: Sum < typenum :: consts :: U274877906944 , typenum :: Sum < typenum :: consts :: U137438953472 , typenum :: Sum < typenum :: consts :: U68719476736 , typenum :: Sum < typenum :: consts :: U8589934592 , typenum :: Sum < typenum :: consts :: U4294967296 , typenum :: Sum < typenum :: consts :: U268435456 , typenum :: Sum < typenum :: consts :: U4194304 , typenum :: Sum < typenum :: consts :: U2097152 , typenum :: Sum < typenum :: consts :: U1048576 , typenum :: Sum < typenum :: consts :: U524288 , typenum :: Sum < typenum :: consts :: U131072 , typenum :: Sum < typenum :: consts :: U8192 , typenum :: Sum < typenum :: consts :: U4096 , typenum :: Sum < typenum :: consts :: U2048 , typenum :: Sum < typenum :: consts :: U1024 , typenum :: Sum < typenum :: consts :: U512 , typenum :: Sum < typenum :: consts :: U256 , typenum :: Sum < typenum :: consts :: U128 , typenum :: Sum < typenum :: consts :: U64 , typenum :: Sum < typenum :: consts :: U32 , typenum :: Sum < typenum :: consts :: U16 , typenum :: Sum < typenum :: consts :: U8 , typenum :: Sum < typenum :: consts :: U4 , typenum :: Sum < typenum :: consts :: U2 , typenum :: Sum < typenum :: consts :: U1 , typenum :: consts :: U0 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ;
type P99999999999999 = typenum :: Sum < typenum :: consts :: P70368744177664 , typenum :: Sum < typenum :: consts :: P17592186044416 , typenum :: Sum < typenum :: consts :: P8796093022208 , typenum :: Sum < typenum :: consts :: P2199023255552 , typenum :: Sum < typenum :: consts :: P549755813888 , typenum :: Sum < typenum :: consts :: P274877906944 , typenum :: Sum < typenum :: consts :: P137438953472 , typenum :: Sum < typenum :: consts :: P68719476736 , typenum :: Sum < typenum :: consts :: P8589934592 , typenum :: Sum < typenum :: consts :: P4294967296 , typenum :: Sum < typenum :: consts :: P268435456 , typenum :: Sum < typenum :: consts :: P4194304 , typenum :: Sum < typenum :: consts :: P2097152 , typenum :: Sum < typenum :: consts :: P1048576 , typenum :: Sum < typenum :: consts :: P524288 , typenum :: Sum < typenum :: consts :: P131072 , typenum :: Sum < typenum :: consts :: P8192 , typenum :: Sum < typenum :: consts :: P4096 , typenum :: Sum < typenum :: consts :: P2048 , typenum :: Sum < typenum :: consts :: P1024 , typenum :: Sum < typenum :: consts :: P512 , typenum :: Sum < typenum :: consts :: P256 , typenum :: Sum < typenum :: consts :: P128 , typenum :: Sum < typenum :: consts :: P64 , typenum :: Sum < typenum :: consts :: P32 , typenum :: Sum < typenum :: consts :: P16 , typenum :: Sum < typenum :: consts :: P8 , typenum :: Sum < typenum :: consts :: P4 , typenum :: Sum < typenum :: consts :: P2 , typenum :: Sum < typenum :: consts :: P1 , typenum :: consts :: Z0 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > ;

Note that negative numbers tyint!(-314159) are not understood by the macro. I think minor change can fix this.

[est31]

@jerry73204 you meant to link rust-lang/rust#63931 right?

[jerry73204]

Yes, exactly.

[dtolnay]

If you want this to work earlier than the expression-position proc macro stabilization, it should be pretty easy to make it work with proc-macro-hack.

[WaffleLapkin]

@jerry73204 it seems like proc-macro in type position got stabilized 1 October 2019 — half a year ago. Do you plan to update your demo / open a PR with tyint! macro to this repo?

[jerry73204]

@WaffleLapkin New changes are made in #136. Now it's still in PR queue.

Edit: typo