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

//! Assert an expression is equal to another.
//!
//! * If true, return Result `Ok(())`.
//!
//! * Otherwise, return Result `Err` with a diagnostic message.
//!
//! This macro provides the same statements as [`assert_`](macro.assert_.html),
//! except this macro returns a Result, rather than doing a panic.
//!
//! This macro is useful for runtime checks, such as checking parameters,
//! or sanitizing inputs, or handling different results in different ways.
//!
//! # Module macros
//!
//! * [`assert_eq`](macro.assert_eq.html)
//! * [`assert_eq_as_result`](macro.assert_eq_as_result.html)
//! * [`debug_assert_eq`](macro.debug_assert_eq.html)

/// Assert an expression is equal to another.
///
/// * If true, return Result `Ok(())`.
///
/// * Otherwise, return Result `Err` with a diagnostic message.
///
/// This macro provides the same statements as [`assert_`](macro.assert_.html),
/// except this macro returns a Result, rather than doing a panic.
///
/// This macro is useful for runtime checks, such as checking parameters,
/// or sanitizing inputs, or handling different results in different ways.
///
/// # Module macros
///
/// * [`assert_eq`](macro.assert_eq.html)
/// * [`assert_eq_as_result`](macro.assert_eq_as_result.html)
/// * [`debug_assert_eq`](macro.debug_assert_eq.html)
///
#[macro_export]
macro_rules! assert_eq_as_result {
    ($a:expr, $b:expr $(,)?) => {{
        match (&$a, &$b) {
            (a_val, b_val) => {
                if a_val == b_val {
                    Ok(())
                } else {
                    Err(format!(
                        concat!(
                            "assertion failed: `assert_eq!(left, right)`\n",
                            "  left label: `{}`,\n",
                            "  left debug: `{:?}`,\n",
                            " right label: `{}`,\n",
                            " right debug: `{:?}`,\n",
                            "        left: `{:?}`,\n",
                            "       right: `{:?}`"
                        ),
                        stringify!($a),
                        $a,
                        stringify!($b),
                        $b,
                        a_val,
                        b_val
                    ))
                }
            }
        }
    }};
}

#[cfg(test)]
mod tests {

    #[test]
    fn test_assert_eq_as_result_x_success() {
        let a: i32 = 1;
        let b: i32 = 1;
        let x = assert_eq_as_result!(a, b);
        assert_eq!(x, Ok(()));
    }

    #[test]
    fn test_assert_eq_as_result_x_failure() {
        let a: i32 = 1;
        let b: i32 = 2;
        let x = assert_eq_as_result!(a, b);
        assert!(x.is_err());
        assert_eq!(
            x.unwrap_err(),
            concat!(
                "assertion failed: `assert_eq!(left, right)`\n",
                "  left label: `a`,\n",
                "  left debug: `1`,\n",
                " right label: `b`,\n",
                " right debug: `2`,\n",
                "        left: `1`,\n",
                "       right: `2`"
            )
        );
    }
}

/// Assert an expression is equal to an expression.
///
/// This macro provides the same statements as [`assert_eq`](macro.assert_eq.html),
/// except this macro's statements are only enabled in non-optimized
/// builds by default. An optimized build will not execute this macro's
/// statements unless `-C debug-assertions` is passed to the compiler.
///
/// This macro is useful for checks that are too expensive to be present
/// in a release build but may be helpful during development.
///
/// The result of expanding this macro is always type checked.
///
/// An unchecked assertion allows a program in an inconsistent state to
/// keep running, which might have unexpected consequences but does not
/// introduce unsafety as long as this only happens in safe code. The
/// performance cost of assertions, however, is not measurable in general.
/// Replacing `assert*!` with `debug_assert*!` is thus only encouraged
/// after thorough profiling, and more importantly, only in safe code!
///
/// This macro is intended to work in a similar way to
/// [`std::debug_assert`](https://doc.rust-lang.org/std/macro.debug_assert.html).
///
/// # Module macros
///
/// * [`assert_eq`](macro.assert_eq.html)
/// * [`assert_eq`](macro.assert_eq.html)
/// * [`debug_assert_eq`](macro.debug_assert_eq.html)
///
#[macro_export]
macro_rules! debug_assert_eq {
    ($($arg:tt)*) => {
        if $crate::cfg!(debug_assertions) {
            $crate::assert_eq!($($arg)*);
        }
    };
}