Trait rand_functors::RandomVariable
source · pub trait RandomVariable: Sizedwhere
Standard: Distribution<Self>,{
// Required method
fn sample_space() -> impl Iterator<Item = Self>;
}Expand description
A type that is enumerable and can be sampled from uniformly.
This trait requires that an implementor also implement
Distribution<Self>, to ensure that it can be sampled from. Additionally,
a sample_space associated function must be provided.
Note that a non-uniform distribution or a non-exhaustive sample space will
result in a logic error. In particular, this means that this trait should
not be implemented for Option<T>, as the probability of None
being sampled is 0.5, regardless of the cardinality of the sample space of
T.
§Provided Implementations
This crate provides implementations of RandomVariable for bool and all
twelve built-in integer types.
Implementations are provided for u32, u64, u128, usize,
i32, i64, i128, and isize strictly for sampling from ranges
(through RandomStrategy::fmap_rand_range). The use of
RandomStrategy::fmap_rand with a 32-bit integer RandomVariable would
involve, at minimum, a 4 GiB allocation just to enumerate the outcomes of a
random process. This is obviously intractable on current computers.
§Implementing RandomVariable
Neither Distribution<T> for Standard nor RandomVariable for T are
derivable. However, implementations for simple structs tends to follow a
pattern. Distribution<Self> implementations will typically call
self.sample(rng) for each field of the struct. RandomVariable
implementations will typically use Iterator::flat_map to create a
Cartesian product of all the sample spaces of the struct’s fields.
use rand::distributions::Standard;
use rand::prelude::*;
use rand_functors::RandomVariable;
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
struct Coordinate {
x: u8,
y: u8,
}
impl Distribution<Coordinate> for Standard {
fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Coordinate {
Coordinate {
x: self.sample(rng),
y: self.sample(rng),
}
}
}
impl RandomVariable for Coordinate {
fn sample_space() -> impl Iterator<Item = Self> {
u8::sample_space().flat_map(|x| u8::sample_space().map(move |y| Coordinate { x, y }))
}
}Required Methods§
sourcefn sample_space() -> impl Iterator<Item = Self>
fn sample_space() -> impl Iterator<Item = Self>
Produce an Iterator containing all possible values of this type.
This iterator must be finite, though a trait bound of
ExactSizeIterator is not specified, to allow the use of
Iterator::flat_map in implementations of this trait.