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#1059 in Magic Beans

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Used in 427 crates (8 directly)

Apache-2.0

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SPL Discriminator

This library allows for easy management of 8-byte discriminators.

The ArrayDiscriminator Struct

With this crate, you can leverage the ArrayDiscriminator type to manage an 8-byte discriminator for generic purposes.

let my_discriminator = ArrayDiscriminator::new([8, 5, 1, 56, 10, 53, 9, 198]);

The new(..) function is also a constant function, so you can use ArrayDiscriminator in constants as well.

const MY_DISCRIMINATOR: ArrayDiscriminator = ArrayDiscriminator::new([8, 5, 1, 56, 10, 53, 9, 198]);

The ArrayDiscriminator struct also offers another constant function as_slice(&self), so you can use as_slice() in constants as well.

const MY_DISCRIMINATOR_SLICE: &[u8] = MY_DISCRIMINATOR.as_slice();

The SplDiscriminate Trait

A trait, SplDiscriminate is also available, which will give you the ArrayDiscriminator constant type and also a slice representation of the discriminator. This can be particularly handy with match statements.

/// A trait for managing 8-byte discriminators in a slab of bytes
pub trait SplDiscriminate {
    /// The 8-byte discriminator as a `[u8; 8]`
    const SPL_DISCRIMINATOR: ArrayDiscriminator;
    /// The 8-byte discriminator as a slice (`&[u8]`)
    const SPL_DISCRIMINATOR_SLICE: &'static [u8] = Self::SPL_DISCRIMINATOR.as_slice();
}

The SplDiscriminate Derive Macro

The SplDiscriminate derive macro is a particularly useful tool for those who wish to derive their 8-byte discriminator from a particular string literal. Typically, you would have to run a hash function against the string literal, then copy the first 8 bytes, and then hard-code those bytes into a statement like the one above.

Instead, you can simply annotate a struct or enum with SplDiscriminate and provide a hash input via the discriminator_hash_input attribute, and the macro will automatically derive the 8-byte discriminator for you!

#[derive(SplDiscriminate)] // Implements `SplDiscriminate` for your struct/enum using your declared string literal hash_input
#[discriminator_hash_input("some_discriminator_hash_input")]
pub struct MyInstruction1 {
    arg1: String,
    arg2: u8,
}

let my_discriminator: ArrayDiscriminator = MyInstruction1::SPL_DISCRIMINATOR;
let my_discriminator_slice: &[u8] = MyInstruction1::SPL_DISCRIMINATOR_SLICE;

Note: the 8-byte discriminator derived using the macro is always the first 8 bytes of the resulting hashed bytes.

Dependencies

~11–19MB
~265K SLoC