predicates/
function.rs

Help
1// Copyright (c) 2018 The predicates-rs Project Developers.
2//
3// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
4// http://www.apache.org/license/LICENSE-2.0> or the MIT license
5// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
6// option. This file may not be copied, modified, or distributed
7// except according to those terms.
8
9//! Definition of `Predicate` for wrapping a `Fn(&T) -> bool`
10
11use std::fmt;
12use std::marker::PhantomData;
13
14use crate::reflection;
15use crate::utils;
16use crate::Predicate;
17
18/// Predicate that wraps a function over a reference that returns a `bool`.
19/// This type is returned by the `predicate::function` function.
20#[allow(clippy::derive_partial_eq_without_eq)]
21#[derive(Debug, Clone, Copy, PartialEq, Eq)]
22pub struct FnPredicate<F, T>
23where
24    F: Fn(&T) -> bool,
25    T: ?Sized,
26{
27    function: F,
28    name: &'static str,
29    _phantom: PhantomData<T>,
30}
31
32unsafe impl<F, T> Send for FnPredicate<F, T>
33where
34    F: Send + Fn(&T) -> bool,
35    T: ?Sized,
36{
37}
38
39unsafe impl<F, T> Sync for FnPredicate<F, T>
40where
41    F: Sync + Fn(&T) -> bool,
42    T: ?Sized,
43{
44}
45
46impl<F, T> FnPredicate<F, T>
47where
48    F: Fn(&T) -> bool,
49    T: ?Sized,
50{
51    /// Provide a descriptive name for this function.
52    ///
53    /// # Examples
54    ///
55    /// ```
56    /// use predicates::prelude::*;
57    ///
58    /// struct Example {
59    ///     string: String,
60    ///     number: i32,
61    /// }
62    ///
63    /// let string_check = predicate::function(|x: &Example| x.string == "hello")
64    ///     .fn_name("is_hello");
65    /// println!("predicate: {}", string_check);
66    /// ```
67    pub fn fn_name(mut self, name: &'static str) -> Self {
68        self.name = name;
69        self
70    }
71}
72
73impl<F, T> Predicate<T> for FnPredicate<F, T>
74where
75    F: Fn(&T) -> bool,
76    T: ?Sized,
77{
78    fn eval(&self, variable: &T) -> bool {
79        (self.function)(variable)
80    }
81
82    fn find_case<'a>(&'a self, expected: bool, variable: &T) -> Option<reflection::Case<'a>> {
83        utils::default_find_case(self, expected, variable)
84    }
85}
86
87impl<F, T> reflection::PredicateReflection for FnPredicate<F, T>
88where
89    F: Fn(&T) -> bool,
90    T: ?Sized,
91{
92}
93
94impl<F, T> fmt::Display for FnPredicate<F, T>
95where
96    F: Fn(&T) -> bool,
97    T: ?Sized,
98{
99    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
100        let palette = crate::Palette::new(f.alternate());
101        write!(
102            f,
103            "{}({})",
104            palette.description(self.name),
105            palette.var("var"),
106        )
107    }
108}
109
110/// Creates a new predicate that wraps over the given function. The returned
111/// type implements `Predicate` and therefore has all combinators available to
112/// it.
113///
114/// # Examples
115///
116/// ```
117/// use predicates::prelude::*;
118///
119/// struct Example {
120///     string: String,
121///     number: i32,
122/// }
123///
124/// let string_check = predicate::function(|x: &Example| x.string == "hello");
125/// let number_check = predicate::function(|x: &Example| x.number == 42);
126/// let predicate_fn = string_check.and(number_check);
127/// let good_example = Example { string: "hello".into(), number: 42 };
128/// assert_eq!(true, predicate_fn.eval(&good_example));
129/// let bad_example = Example { string: "goodbye".into(), number: 0 };
130/// assert_eq!(false, predicate_fn.eval(&bad_example));
131/// ```
132pub fn function<F, T>(function: F) -> FnPredicate<F, T>
133where
134    F: Fn(&T) -> bool,
135    T: ?Sized,
136{
137    FnPredicate {
138        function,
139        name: "fn",
140        _phantom: PhantomData,
141    }
142}
143
144#[test]
145fn str_function() {
146    let f = function(|x: &str| x == "hello");
147    assert!(f.eval("hello"));
148    assert!(!f.eval("goodbye"));
149}
predicates/function.rs

predicates/
function.rs
