generic-array

This crate implements a structure that can be used as a generic array type.

**Requires minimum Rust version of 1.65.0

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Upgrading from 0.14 or using with hybrid-array 0.4

generic-array 0.14 has been officially deprecated, so here's a quick guide on how to upgrade from generic-array 0.14 to 1.x. Note that libraries depending on generic-array will need to update their usage as well. Some libraries are moving to hybrid-array 0.4 instead, which we provide interoperability with generic-array 1.x via the hybrid-array-0_4 feature flag.

To upgrade to 1.x, change your Cargo.toml to use the new version:

[dependencies]
generic-array = "1"

then in your code, go through and remove the <T> from ArrayLength<T> bounds, as the type parameter has been removed. It's now just ArrayLength.

If you need to interoperate with generic-array 0.14, enable the compat-0_14 feature flag:

[dependencies]
generic-array = { version = "1", features = ["compat-0_14"] }

then use the to_0_14/from_0_14/as_0_14/as_0_14_mut methods on GenericArray to convert between versions, or use the From/AsRef/AsMut implementations.

The arr! macro has changed to no longer require a type parameter, so change:

let array = arr![i32; 1, 2, 3];
// to
let array = arr![1, 2, 3];

For interoperability with hybrid-array 0.4, enable the hybrid-array-0_4 feature flag:

[dependencies]
generic-array = { version = "1", features = ["hybrid-array-0_4"] }

then use the to_ha0_4/from_ha0_4/as_ha0_4/as_ha0_4_mut methods on GenericArray to convert between versions, or use the From/AsRef/AsMut implementations.

We also implement the AssocArraySize and AsArrayRef/AsArrayMut traits from hybrid-array for GenericArray.

Usage

Before Rust 1.51, arrays [T; N] were problematic in that they couldn't be generic with respect to the length N, so this wouldn't work:

struct Foo<N> {
    data: [i32; N],
}

Since 1.51, the below syntax is valid:

struct Foo<const N: usize> {
    data: [i32; N],
}

However, the const-generics we have as of writing this are still the minimum-viable product (min_const_generics), so many situations still result in errors, such as this example:

trait Bar {
    const LEN: usize;

    // Error: cannot perform const operation using `Self`
    fn bar(&self) -> Foo<{ Self::LEN }>;
}

generic-array defines a new trait ArrayLength and a struct GenericArray<T, N: ArrayLength>, which lets the above be implemented as:

struct Foo<N: ArrayLength> {
    data: GenericArray<i32, N>
}

trait Bar {
    type LEN: ArrayLength;
    fn bar(&self) -> Foo<Self::LEN>;
}

The ArrayLength trait is implemented for unsigned integer types from typenum crate. For example, GenericArray<T, U5> would work almost like [T; 5]:

use generic_array::typenum::U5;

struct Foo<T, N: ArrayLength> {
    data: GenericArray<T, N>
}

let foo = Foo::<i32, U5> { data: GenericArray::default() };

The arr! macro is provided to allow easier creation of literal arrays, as shown below:

let array = arr![1, 2, 3];
//  array: GenericArray<i32, typenum::U3>
assert_eq!(array[2], 3);

Feature flags

[dependencies.generic-array]
features = [
    "serde",            # Serialize/Deserialize implementation
    "zeroize",          # Zeroize implementation for setting array elements to zero
    "const-default",    # Compile-time const default value support via trait
    "alloc",            # Enables From/TryFrom implementations between GenericArray and Vec<T>/Box<[T]>
    "faster-hex",       # Enables internal use of the `faster-hex` crate for faster hex encoding via SIMD
    "compat-0_14",      # Enables interoperability with `generic-array` 0.14
    "hybrid-array-0_4"  # Enables interoperability with `hybrid-array` 0.4
]