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 a constant (always true or always false) `Predicate`.
10
11 use std::fmt;
12
13 use crate::reflection;
14 use crate::utils;
15 use crate::Predicate;
16
17 /// Predicate that always returns a constant (boolean) result.
18 ///
19 /// This is created by the `predicate::always` and `predicate::never` functions.
20 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
21 pub struct BooleanPredicate {
22 retval: bool,
23 }
24
25 impl<Item: ?Sized> Predicate<Item> for BooleanPredicate {
eval(&self, _variable: &Item) -> bool26 fn eval(&self, _variable: &Item) -> bool {
27 self.retval
28 }
29
find_case<'a>(&'a self, expected: bool, variable: &Item) -> Option<reflection::Case<'a>>30 fn find_case<'a>(&'a self, expected: bool, variable: &Item) -> Option<reflection::Case<'a>> {
31 utils::default_find_case(self, expected, variable)
32 }
33 }
34
35 impl reflection::PredicateReflection for BooleanPredicate {
parameters<'a>(&'a self) -> Box<dyn Iterator<Item = reflection::Parameter<'a>> + 'a>36 fn parameters<'a>(&'a self) -> Box<dyn Iterator<Item = reflection::Parameter<'a>> + 'a> {
37 let params = vec![reflection::Parameter::new("value", &self.retval)];
38 Box::new(params.into_iter())
39 }
40 }
41
42 impl fmt::Display for BooleanPredicate {
fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result43 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
44 let palette = crate::Palette::new(f.alternate());
45 write!(f, "{}", palette.expected(self.retval))
46 }
47 }
48
49 /// Creates a new `Predicate` that always returns `true`.
50 ///
51 /// # Examples
52 ///
53 /// ```
54 /// use predicates::prelude::*;
55 ///
56 /// let predicate_fn = predicate::always();
57 /// assert_eq!(true, predicate_fn.eval(&5));
58 /// assert_eq!(true, predicate_fn.eval(&10));
59 /// assert_eq!(true, predicate_fn.eval(&15));
60 /// // Won't work - Predicates can only operate on a single type
61 /// // assert_eq!(true, predicate_fn.eval("hello"))
62 /// ```
always() -> BooleanPredicate63 pub fn always() -> BooleanPredicate {
64 BooleanPredicate { retval: true }
65 }
66
67 /// Creates a new `Predicate` that always returns `false`.
68 ///
69 /// # Examples
70 ///
71 /// ```
72 /// use predicates::prelude::*;
73 ///
74 /// let predicate_fn = predicate::never();
75 /// assert_eq!(false, predicate_fn.eval(&5));
76 /// assert_eq!(false, predicate_fn.eval(&10));
77 /// assert_eq!(false, predicate_fn.eval(&15));
78 /// // Won't work - Predicates can only operate on a single type
79 /// // assert_eq!(false, predicate_fn.eval("hello"))
80 /// ```
never() -> BooleanPredicate81 pub fn never() -> BooleanPredicate {
82 BooleanPredicate { retval: false }
83 }
84