Trait ValueTree

Source

pub trait ValueTree {
    type Value: Debug;

    // Required methods
    fn current(&self) -> Self::Value;
    fn simplify(&mut self) -> bool;
    fn complicate(&mut self) -> bool;
}

Expand description

A generated value and its associated shrinker.

Conceptually, a ValueTree represents a spectrum between a “minimally complex” value and a starting, randomly-chosen value. For values such as numbers, this can be thought of as a simple binary search, and this is how the ValueTree state machine is defined.

The ValueTree state machine notionally has three fields: low, current, and high. Initially, low is the “minimally complex” value for the type, and high and current are both the initially chosen value. It can be queried for its current state. When shrinking, the controlling code tries simplifying the value one step. If the test failure still happens with the simplified value, further simplification occurs. Otherwise, the code steps back up towards the prior complexity.

The main invariants here are that the “high” value always corresponds to a failing test case, and that repeated calls to complicate() will return false only once the “current” value has returned to what it was before the last call to simplify().

While it would be possible for default do-nothing implementations of simplify() and complicate() to be provided, this was not done deliberately since the majority of strategies will want to define their own shrinking anyway, and the minority that do not must call it out explicitly by their own implementation.

Required Associated Types§

Source

type Value: Debug

The type of the value produced by this ValueTree.

Required Methods§

Source

fn current(&self) -> Self::Value

Returns the current value.

Source

fn simplify(&mut self) -> bool

Attempts to simplify the current value. Notionally, this sets the “high” value to the current value, and the current value to a “halfway point” between high and low, rounding towards low.

Returns whether any state changed as a result of this call. This does not necessarily imply that the value of current() has changed, since in the most general case, it is not possible for an implementation to determine this.

This call needs to correctly handle being called even immediately after it had been called previously and returned false.

Source

fn complicate(&mut self) -> bool

Attempts to partially undo the last simplification. Notionally, this sets the “low” value to one plus the current value, and the current value to a “halfway point” between high and the new low, rounding towards low.

Returns whether any state changed as a result of this call. This does not necessarily imply that the value of current() has changed, since in the most general case, it is not possible for an implementation to determine this.

It is usually expected that, immediately after a call to simplify() which returns true, this call will itself return true. However, this is not always the case; in some strategies, particularly those that use some form of rejection sampling, the act of trying to simplify may change the state such that simplify() returns true, yet ultimately left the resulting value unchanged, in which case there is nothing left to complicate.

This call does not need to gracefully handle being called before simplify() was ever called, but does need to correctly handle being called even immediately after it had been called previously and returned false.

Trait ValueTreeCopy item path

Required Associated Types§

type Value: Debug

Required Methods§

fn current(&self) -> Self::Value

fn simplify(&mut self) -> bool

fn complicate(&mut self) -> bool

Implementations on Foreign Types§

impl<T: Debug> ValueTree for fn() -> T

type Value = T

fn simplify(&mut self) -> bool

fn complicate(&mut self) -> bool

fn current(&self) -> Self::Value

impl<T: ValueTree + ?Sized> ValueTree for Box<T>

type Value = <T as ValueTree>::Value

fn current(&self) -> Self::Value

fn simplify(&mut self) -> bool

fn complicate(&mut self) -> bool

Implementors§

impl ValueTree for BoolValueTree

type Value = bool

impl ValueTree for CharValueTree

type Value = char

impl ValueTree for proptest::num::f32::BinarySearch

type Value = f32

impl ValueTree for proptest::num::f64::BinarySearch

type Value = f64

impl ValueTree for proptest::num::i8::BinarySearch

type Value = i8

impl ValueTree for proptest::num::i16::BinarySearch

type Value = i16

impl ValueTree for proptest::num::i32::BinarySearch

type Value = i32

impl ValueTree for proptest::num::i64::BinarySearch

type Value = i64

impl ValueTree for proptest::num::i128::BinarySearch

type Value = i128

impl ValueTree for proptest::num::isize::BinarySearch

type Value = isize

impl ValueTree for proptest::num::u8::BinarySearch

type Value = u8

impl ValueTree for proptest::num::u16::BinarySearch

type Value = u16

impl ValueTree for proptest::num::u32::BinarySearch

type Value = u32

impl ValueTree for proptest::num::u64::BinarySearch

type Value = u64

impl ValueTree for proptest::num::u128::BinarySearch

type Value = u128

impl ValueTree for proptest::num::usize::BinarySearch

type Value = usize

impl ValueTree for IndexValueTree

type Value = Index

impl ValueTree for SelectorValueTree

type Value = Selector

impl<A: Strategy, B: Strategy<Value = A::Value>> ValueTree for TupleUnionValueTree<(LazyValueTree<A>, Option<LazyValueTree<B>>)>

type Value = <A as Strategy>::Value

impl<A: Strategy, B: Strategy<Value = A::Value>, C: Strategy<Value = A::Value>> ValueTree for TupleUnionValueTree<(LazyValueTree<A>, Option<LazyValueTree<B>>, Option<LazyValueTree<C>>)>

type Value = <A as Strategy>::Value

impl<A: Strategy, B: Strategy<Value = A::Value>, C: Strategy<Value = A::Value>, D: Strategy<Value = A::Value>> ValueTree for TupleUnionValueTree<(LazyValueTree<A>, Option<LazyValueTree<B>>, Option<LazyValueTree<C>>, Option<LazyValueTree<D>>)>

type Value = <A as Strategy>::Value

impl<A: Strategy, B: Strategy<Value = A::Value>, C: Strategy<Value = A::Value>, D: Strategy<Value = A::Value>, E: Strategy<Value = A::Value>> ValueTree for TupleUnionValueTree<(LazyValueTree<A>, Option<LazyValueTree<B>>, Option<LazyValueTree<C>>, Option<LazyValueTree<D>>, Option<LazyValueTree<E>>)>

type Value = <A as Strategy>::Value

type Value = <A as Strategy>::Value

type Value = <A as Strategy>::Value

type Value = <A as Strategy>::Value

type Value = <A as Strategy>::Value

type Value = <A as Strategy>::Value

impl<A: ValueTree> ValueTree for TupleValueTree<(A,)>

type Value = (<A as ValueTree>::Value,)

impl<A: ValueTree, B: ValueTree> ValueTree for TupleValueTree<(A, B)>

type Value = (<A as ValueTree>::Value, <B as ValueTree>::Value)

impl<A: ValueTree, B: ValueTree, C: ValueTree> ValueTree for TupleValueTree<(A, B, C)>

type Value = (<A as ValueTree>::Value, <B as ValueTree>::Value, <C as ValueTree>::Value)

impl<A: ValueTree, B: ValueTree, C: ValueTree, D: ValueTree> ValueTree for TupleValueTree<(A, B, C, D)>

type Value = (<A as ValueTree>::Value, <B as ValueTree>::Value, <C as ValueTree>::Value, <D as ValueTree>::Value)

impl<A: ValueTree, B: ValueTree, C: ValueTree, D: ValueTree, E: ValueTree> ValueTree for TupleValueTree<(A, B, C, D, E)>

type Value = (<A as ValueTree>::Value, <B as ValueTree>::Value, <C as ValueTree>::Value, <D as ValueTree>::Value, <E as ValueTree>::Value)

impl<A: ValueTree, B: ValueTree, C: ValueTree, D: ValueTree, E: ValueTree, F: ValueTree> ValueTree for TupleValueTree<(A, B, C, D, E, F)>

type Value = (<A as ValueTree>::Value, <B as ValueTree>::Value, <C as ValueTree>::Value, <D as ValueTree>::Value, <E as ValueTree>::Value, <F as ValueTree>::Value)

Trait ValueTree

impl<K, V> ValueTree for BTreeMapValueTree<K, V>
where K: ValueTree, V: ValueTree, K::Value: Ord,

impl<K, V> ValueTree for HashMapValueTree<K, V>
where K: ValueTree, V: ValueTree, K::Value: Hash + Eq,

impl<S: ValueTree> ValueTree for FlattenValueTree<S>
where S::Value: Strategy,

impl<S: ValueTree, O: Debug> ValueTree for MapInto<S, O>
where S::Value: Into<O>,

impl<T> ValueTree for BTreeSetValueTree<T>
where T: ValueTree, T::Value: Ord,

impl<T> ValueTree for BinaryHeapValueTree<T>
where T: ValueTree, T::Value: Ord,

impl<T> ValueTree for HashSetValueTree<T>
where T: ValueTree, T::Value: Hash + Eq,

impl<T> ValueTree for LinkedListValueTree<T>
where T: ValueTree,

impl<T> ValueTree for VecDequeValueTree<T>
where T: ValueTree,

impl<T> ValueTree for OptionValueTree<T>
where T: Strategy,

impl<T> ValueTree for SelectValueTree<T>
where T: Clone + Debug + 'static,

impl<T> ValueTree for RegexGeneratorValueTree<T>
where T: Debug,

impl<T, E> ValueTree for MaybeErrValueTree<T, E>
where T: Strategy, E: Strategy,

impl<T, E> ValueTree for MaybeOkValueTree<T, E>
where T: Strategy, E: Strategy,