proptest/strategy/
just.rs

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
//-
// Copyright 2017, 2018 The proptest developers
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use crate::std_facade::fmt;

use crate::strategy::{NewTree, Strategy, ValueTree};
use crate::test_runner::TestRunner;

macro_rules! noshrink {
    () => {
        fn simplify(&mut self) -> bool {
            false
        }
        fn complicate(&mut self) -> bool {
            false
        }
    };
}

//==============================================================================
// Just
//==============================================================================

/// A `Strategy` which always produces a single value value and never
/// simplifies.
#[derive(Clone, Copy, Debug)]
#[must_use = "strategies do nothing unless used"]
pub struct Just<T: Clone + fmt::Debug>(
    /// The value produced by this strategy.
    pub T,
);

impl<T: Clone + fmt::Debug> Strategy for Just<T> {
    type Tree = Self;
    type Value = T;

    fn new_tree(&self, _: &mut TestRunner) -> NewTree<Self> {
        Ok(self.clone())
    }
}

impl<T: Clone + fmt::Debug> ValueTree for Just<T> {
    type Value = T;
    noshrink!();
    fn current(&self) -> T {
        self.0.clone()
    }
}

//==============================================================================
// LazyJust
//==============================================================================

/// A `Strategy` which always produces a single value value and never
/// simplifies. If `T` is `Clone`, you should use `Just` instead.
///
/// This is a generalization of `Just` and works by calling
/// the provided `Fn () -> T` in `.current()` every time. This is not a
/// very interesting strategy, but is required in cases where `T` is
/// not `Clone`. It is also used in `proptest_derive` where we can't
/// assume that your type is `Clone`.
///
/// **It is important that the function used be pure.**
#[must_use = "strategies do nothing unless used"]
pub struct LazyJust<T, F: Fn() -> T> {
    /// The function executed in `.current()`.
    function: F,
}

/// Shorthand for `LazyJust<T, fn () -> T>`.
pub type LazyJustFn<V> = LazyJust<V, fn() -> V>;

impl<T, F: Fn() -> T> LazyJust<T, F> {
    /// Constructs a `LazyJust` strategy given the function/closure
    /// that produces the value.
    ///
    /// **It is important that the function used be pure.**
    pub fn new(function: F) -> Self {
        Self { function }
    }
}

impl<T: fmt::Debug, F: Clone + Fn() -> T> Strategy for LazyJust<T, F> {
    type Tree = Self;
    type Value = T;

    fn new_tree(&self, _: &mut TestRunner) -> NewTree<Self> {
        Ok(self.clone())
    }
}

impl<T: fmt::Debug, F: Fn() -> T> ValueTree for LazyJust<T, F> {
    type Value = T;
    noshrink!();
    fn current(&self) -> Self::Value {
        (self.function)()
    }
}

impl<T, F: Copy + Fn() -> T> Copy for LazyJust<T, F> {}

impl<T, F: Clone + Fn() -> T> Clone for LazyJust<T, F> {
    fn clone(&self) -> Self {
        Self {
            function: self.function.clone(),
        }
    }
}

impl<T, F: Fn() -> T> fmt::Debug for LazyJust<T, F> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("LazyJust")
            .field("function", &"<function>")
            .finish()
    }
}

//==============================================================================
// Any `fn () -> T` is a Strategy
//==============================================================================

// TODO: try 'F: Fn () -> T' instead when we've got specialization.

impl<T: fmt::Debug> Strategy for fn() -> T {
    type Tree = Self;
    type Value = T;

    fn new_tree(&self, _: &mut TestRunner) -> NewTree<Self> {
        Ok(*self)
    }
}

impl<T: fmt::Debug> ValueTree for fn() -> T {
    type Value = T;
    noshrink!();
    fn current(&self) -> Self::Value {
        self()
    }
}