add optional const_generics support

[soruh]

Adds a const_generics feature that uses min_const_generics which will be stabilized on March 25, 2021 as part of Rust 1.51 (and is currently available in beta) to allow for reading/writing arrays with >32 elements when enabled.

[sharksforarms]

This looks great! Thanks!

[soruh]

great, thank you!

[v1gnesh]

Hey @soruh, could you show an example of how this can be used?

[wcampbell0x2a]

Hey @soruh, could you show an example of how this can be used?

This feature is enabled on master:

deku/Cargo.toml

Line 22 in d045596

default = ["std", "const_generics"]

[soruh]

It allows you to use arrays that are more than 32 elements long and arrays with const generic sizes, so this impl

here's an example:

use deku::{DekuContainerRead, DekuContainerWrite, DekuRead, DekuUpdate, DekuWrite};

#[derive(Debug, PartialEq, DekuRead, DekuWrite)]
#[deku(endian = "big")]
struct DekuTest<const N: usize> {
    #[deku(bits = "4")]
    field_a: u8,
    #[deku(bits = "4")]
    field_b: u8,
    field_c: [u8; 40],
    field_d: [u8; N],
}

fn main() {
    const N: usize = 128;

    let mut data = vec![0u8; 1 + 40 + N];
    data[0] = 170;
    data[1..]
        .iter_mut()
        .enumerate()
        .for_each(|(i, x)| *x = i as u8);
    let (_, value) = DekuTest::<N>::from_bytes((data.as_ref(), 0)).unwrap();

    dbg!(value);
}

without the feature this does not compile. It's a only a feature, because const-generics were very new back then and older compiler versions do not support const-generics.

[v1gnesh]

Hey @soruh, could you show an example of how this can be used?

This feature is enabled on master:

deku/Cargo.toml

Line 22 in d045596

default = ["std", "const_generics"]

Do I have to add something to my project's Cargo.toml to make use of this?
I get a squiggly red line under DekuRead when my Struct uses has a field like this:

    field: MoString<n>

where

pub struct MoString<const N: usize> (
    #[deku(map=func)
    String,
);

[soruh]

The feature should is enabled by default, unless you explicitly turned it of with default-features=false or are using an ancient version. I think you probably made a mistake while implementing your MyString type. Also generally, a merged pull request from two years ago is not the greatest place to ask these things... Maybe open a discussion or something and please provide the error you're getting instead of just saying you're getting an error.

[v1gnesh]

Yes, sure, will try to reproduce separately and open a discussion. Thanks for responding here.