greyblake / arbitrary_ext

Provides a way to derive Arbitrary trait but set custom implementation for single fields if necessary.

Arbitrary Ext

Since 1.2.0 Arbitrary supports custom arbitrary implementation for fields on derive.

But it still remains tricky, if a type that does not implement Arbitrary is wrapped into a generic type.

This crate provides s set of function combinators to support the containers and collections form the standard library.

See the example below.

Usage

use arbitrary_ext::{arbitrary_option, arbitrary_vec, arbitrary_hash_map};
use std::collections::HashMap;

// Imagine this is a foreign type, that by some reason does not implement Arbitrary trait.
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct Number(u32);

// Our custom function to generate arbitrary Number out of Unstructured.
fn arbitrary_number(u: &mut Unstructured) -> arbitrary::Result<Number> {
    let value = u.int_in_range(0..=1000)?;
    Ok(Number(value))
}

#[derive(Debug, Arbitrary)]
struct Example {
    #[arbitrary(with = arbitrary_number)]
    number: Number,

    #[arbitrary(with = arbitrary_option(arbitrary_number))]
    option: Option<Number>,

    #[arbitrary(with = arbitrary_vec(arbitrary_number))]
    vec: Vec<Number>,

    #[arbitrary(
        with = arbitrary_hash_map(
            arbitrary_number,
            arbitrary_vec(arbitrary_option(arbitrary_number))
        )
    )]
    hash_map: HashMap<Number, Vec<Option<Number>>>,
}

Without having arbitrary_option, arbitrary_vec, arbitrary_hash_map combinators, would be forced to implement out custom functions to generate arbitrary Option<Number>, Vec<Number> and HashMap<Number, Vec<Option<Number>>>. e.g.:

fn arbitrary_option_number(u: &mut Unstructured) -> arbitrary::Result<Option<Number>>;
fn arbitrary_vec_number(u: &mut Unstructured) -> arbitrary::Result<Vec<Number>>;
fn arbitrary_hash_map_of_numbers(u: &mut Unstructured) -> arbitrary::Result<HashMap<Number, Vec<Option<Number>>>>;

But this becomes tedious very quickly.

History of the crate

Initially the crate was created to workaround this Arbitrary issue but it was later addressed in this PR.