Struct proptest::sample::Index

pub struct Index(/* private fields */);

A stand-in for an index into a slice or similar collection or conceptually similar things.

At the lowest level, Index is a mechanism for generating usize values in the range [0..N), for some N whose value is not known until it is needed. (Contrast with using 0..N itself as a strategy, where you need to know N when you define the strategy.)

For any upper bound, the actual index produced by an Index is the same no matter how many times it is used. Different upper bounds will produce different but not independent values.

Shrinking will cause the index to binary search through the underlying collection(s) it is used to sample.

Note that Index cannot currently be used as a slice index (e.g., slice[index]) due to the trait coherence rules.

Example

If the collection itself being indexed is itself generated by a strategy, you can make separately define that strategy and a strategy generating one or more Indexes and then join the two after input generation, avoiding a call to prop_flat_map().

use proptest::prelude::*;

proptest! {
    #[test]
    fn my_test(
        names in prop::collection::vec("[a-z]+", 10..20),
        indices in prop::collection::vec(any::<prop::sample::Index>(), 5..10)
    ) {
        // We now have Vec<String> of ten to twenty names, and a Vec<Index>
        // of five to ten indices and can combine them however we like.
        for index in &indices {
            println!("Accessing item by index: {}", names[index.index(names.len())]);
            println!("Accessing item by convenience method: {}", index.get(&names));
        }
        // Test stuff...
    }
}

Implementations

impl Index

pub fn index(&self, size: usize) -> usize

Return the real index that would be used to index a collection of size size.

Panics

Panics if size == 0.

pub fn get<'a, T>(&self, slice: &'a [T]) -> &'a T

Return a reference to the element in slice that this Index refers to.

A shortcut for &slice[index.index(slice.len())].

pub fn get_mut<'a, T>(&self, slice: &'a mut [T]) -> &'a mut T

Return a mutable reference to the element in slice that this Index refers to.

A shortcut for &mut slice[index.index(slice.len())].

Trait Implementations

impl Arbitrary for Index

type Parameters = ()

The type of parameters that arbitrary_with accepts for configuration of the generated Strategy. Parameters must implement Default.

type Strategy = IndexStrategy

The type of Strategy used to generate values of type Self.

fn arbitrary_with(_: ()) -> IndexStrategy

Generates a Strategy for producing arbitrary values of type the implementing type (Self). The strategy is passed the arguments given in args.

fn arbitrary() -> Self::Strategy

Generates a Strategy for producing arbitrary values of type the implementing type (Self).

impl Clone for Index

fn clone(&self) -> Index

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Index

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Copy for Index