assertables/assert_in_delta.rs
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//! Assert a number is within delta of another number.
//!
//! Pseudocode:<br>
//! | a - b | ≤ Δ
//!
//! # Example
//!
//! ```rust
//! # #[macro_use] extern crate assertables;
//! # fn main() {
//! let a: i8 = 10;
//! let b: i8 = 11;
//! let delta: i8 = 1;
//! assert_in_delta!(a, b, delta);
//! # }
//! ```
//!
//!
//! ## Comparisons
//!
//! This crate provides macro groups that test approximations and nearness:
//!
//! * [`assert_approx_eq`](macro@crate::assert_approx_eq) and
//! [`assert_approx_ne`](macro@crate::assert_approx_ne) test the approximate
//! equality within 1e-6. The macro name and the approximate value are chosen
//! to be similar to the longtime popular rust crate `assert_approx_eq`.
//!
//! * [`assert_in_delta`](macro@crate::assert_in_delta) tests the absolute error
//! (i.e. delta). This is the magnitude of the difference between the exact
//! value and the approximation.
//!
//! * [`assert_in_epsilon`](macro@crate::assert_in_epsilon) tests the relative
//! error (i.e. epsilon). This is the absolute error divided by the magnitude
//! of the exact value. This can be used to compare approximations of numbers
//! of wildly differing size.
//!
//! Examples:
//!
//! * Approximating the number 100 and 103 has an absolute error (delta) of 3
//! and a relative error (epsilon) of 0.03.
//!
//! * Approximating the number 1,000,000 and 1,000,003 has an absolute error
//! (delta) of 3, and a relative error (espilon) of 0.000003.
//!
//! * For many kinds of applications, the relative error is more important than
//! the absolute error.
//!
//!
//! ## Thanks
//!
//! * Thanks to [Ashley Williams](https://github.com/ashleygwilliams) for
//! creating and maintaining the `assert_approx_eq` crate.
//!
//! * Thanks to [Ryan Davis](https://github.com/zenspider) and Ruby minitest for
//! creating and maintaining `assert_in_delta` and `assert_in_epsilon` code.
//!
//!
//! # Module macros
//!
//! * [`assert_in_delta`](macro@crate::assert_in_delta)
//! * [`assert_in_delta_as_result`](macro@crate::assert_in_delta_as_result)
//! * [`debug_assert_in_delta`](macro@crate::debug_assert_in_delta)
/// Assert a number is within delta of another number.
///
/// Pseudocode:<br>
/// | a - b | ≤ Δ
///
/// * If true, return Result `Ok(())`.
///
/// * When false, return [`Err`] with a message and the values of the
/// expressions with their debug representations.
///
/// 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_in_delta`](macro@crate::assert_in_delta)
/// * [`assert_in_delta_as_result`](macro@crate::assert_in_delta_as_result)
/// * [`debug_assert_in_delta`](macro@crate::debug_assert_in_delta)
///
#[macro_export]
macro_rules! assert_in_delta_as_result {
($a:expr, $b:expr, $delta:expr $(,)?) => {{
match (&$a, &$b, &$delta) {
(a, b, delta) => {
if a == b {
Ok(())
} else {
let diff = if (a > b) { a - b } else { b - a };
if diff <= *delta {
Ok(())
} else {
Err(format!(
concat!(
"assertion failed: `assert_in_delta!(a, b, delta)`\n",
"https://docs.rs/assertables/8.9.0/assertables/macro.assert_in_delta.html\n",
" a label: `{}`,\n",
" a debug: `{:?}`,\n",
" b label: `{}`,\n",
" b debug: `{:?}`,\n",
" delta label: `{}`,\n",
" delta: `{:?}`,\n",
" | a - b |: `{:?}`,\n",
" | a - b | ≤ delta: {}"
),
stringify!($a),
a,
stringify!($b),
b,
stringify!($delta),
delta,
diff,
false
))
}
}
}
}
}};
}
#[cfg(test)]
mod tests {
#[test]
fn test_assert_in_delta_as_result_x_success() {
let a: i8 = 10;
let b: i8 = 11;
let delta: i8 = 1;
let result = assert_in_delta_as_result!(a, b, delta);
assert_eq!(result, Ok(()));
}
#[test]
fn test_assert_in_delta_as_result_x_failure() {
let a: i8 = 10;
let b: i8 = 12;
let delta: i8 = 1;
let result = assert_in_delta_as_result!(a, b, delta);
assert!(result.is_err());
assert_eq!(
result.unwrap_err(),
concat!(
"assertion failed: `assert_in_delta!(a, b, delta)`\n",
"https://docs.rs/assertables/8.9.0/assertables/macro.assert_in_delta.html\n",
" a label: `a`,\n",
" a debug: `10`,\n",
" b label: `b`,\n",
" b debug: `12`,\n",
" delta label: `delta`,\n",
" delta: `1`,\n",
" | a - b |: `2`,\n",
" | a - b | ≤ delta: false"
)
);
}
}
/// Assert a number is within delta of another number.
///
/// Pseudocode:<br>
/// | a - b | ≤ Δ
///
/// * If true, return `()`.
///
/// * Otherwise, call [`panic!`] with a message and the values of the
/// expressions with their debug representations.
///
/// # Examples
///
/// ```rust
/// # #[macro_use] extern crate assertables;
/// # use std::panic;
/// # fn main() {
/// let a: i8 = 10;
/// let b: i8 = 11;
/// let delta: i8 = 1;
/// assert_in_delta!(a, b, delta);
///
/// # let result = panic::catch_unwind(|| {
/// let a: i8 = 10;
/// let b: i8 = 12;
/// let delta: i8 = 1;
/// assert_in_delta!(a, b, delta);
/// # });
/// // assertion failed: `assert_in_delta!(a, b, delta)`
/// // https://docs.rs/assertables/8.9.0/assertables/macro.assert_in_delta.html
/// // a label: `a`,
/// // a debug: `10`,
/// // b label: `b`,
/// // b debug: `12`,
/// // delta label: `delta`,
/// // delta: `1`,
/// // | a - b |: `2`,
/// // | a - b | ≤ delta: false
/// # let actual = result.unwrap_err().downcast::<String>().unwrap().to_string();
/// # let expect = concat!(
/// # "assertion failed: `assert_in_delta!(a, b, delta)`\n",
/// # "https://docs.rs/assertables/8.9.0/assertables/macro.assert_in_delta.html\n",
/// # " a label: `a`,\n",
/// # " a debug: `10`,\n",
/// # " b label: `b`,\n",
/// # " b debug: `12`,\n",
/// # " delta label: `delta`,\n",
/// # " delta: `1`,\n",
/// # " | a - b |: `2`,\n",
/// # " | a - b | ≤ delta: false",
/// # );
/// # assert_eq!(actual, expect);
/// # }
/// ```
///
/// The macros `assert_in_delta` and `assert_in_epsilon` can test
/// approximations:
///
/// * For an approximation, the absolute error (i.e. delta) is the magnitude of
/// the difference between the exact value and the approximation. For this,
/// use the macro
///
/// * For an approximation, the relative error (i.e. epsilon) is the absolute
/// error divided by the magnitude of the exact value. This can be used to
/// compare approximations of numbers of wildly differing size.
///
/// * For example, approximating the number 1,000 with an absolute error of 3
/// is, in most applications, much worse than approximating the number
/// 1,000,000 with an absolute error of 3; in the first case the relative
/// error is 0.003 and in the second it is only 0.000003.
///
/// * Thanks to Ruby minitest for the example and documentation.
///
/// # Module macros
///
/// * [`assert_in_delta`](macro@crate::assert_in_delta)
/// * [`assert_in_delta_as_result`](macro@crate::assert_in_delta_as_result)
/// * [`debug_assert_in_delta`](macro@crate::debug_assert_in_delta)
///
#[macro_export]
macro_rules! assert_in_delta {
($a:expr, $b:expr, $delta:expr $(,)?) => {{
match assert_in_delta_as_result!($a, $b, $delta) {
Ok(()) => (),
Err(err) => panic!("{}", err),
}
}};
($a:expr, $b:expr, $delta:expr, $($message:tt)+) => {{
match assert_in_delta_as_result!($a, $b, $delta) {
Ok(()) => (),
Err(_err) => panic!("{}", $($message)+),
}
}};
}
/// Assert a number is within delta of another number.
///
/// Pseudocode:<br>
/// | a - b | ≤ Δ
///
/// This macro provides the same statements as [`assert_in_delta`](macro.assert_in_delta.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_in_delta`](macro@crate::assert_in_delta)
/// * [`assert_in_delta`](macro@crate::assert_in_delta)
/// * [`debug_assert_in_delta`](macro@crate::debug_assert_in_delta)
///
#[macro_export]
macro_rules! debug_assert_in_delta {
($($arg:tt)*) => {
if $crate::cfg!(debug_assertions) {
$crate::assert_in_delta!($($arg)*);
}
};
}