Struct Unknown 

pub struct Unknown;

Used with generic types in expectations where the concrete type is not relevant for the failure message.

This type implements the std format trait std::fmt::Debug and std::fmt::Display which both format the value as “_”.

assert_that!(format!("{:?}", Unknown)).is_equal_to("_");
assert_that!(format!("{}", Unknown)).is_equal_to("_");

Examples

This type is used to implement the expectations

• IsSome
• IsNone
• IsOk
• IsErr

For example for implementing the function Expectation::message() for the IsOk expectation for Result<T, E> the concrete types for T and E are not relevant. The implementation of the trait looks like this:

impl<T, E> Expectation<Result<T, E>> for IsOk
where
    T: Debug,
    E: Debug,
{
    fn test(&mut self, subject: &Result<T, E>) -> bool {
        subject.is_ok()
    }

    fn message(&self, expression: &Expression<'_>, actual: &Result<T, E>, _inverted: bool, _format: &DiffFormat) -> String {
        format!(
            "expected {expression} is {:?}\n   but was: {actual:?}\n  expected: {:?}",
            Ok::<_, Unknown>(Unknown),
            Ok::<_, Unknown>(Unknown),
        )
    }
}

Trait Implementations

impl Clone for Unknown

fn clone(&self) -> Unknown

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Unknown

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Unknown

fn default() -> Unknown

Returns the “default value” for a type.

impl Display for Unknown

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Unknown

fn eq(&self, other: &Unknown) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for Unknown

impl Eq for Unknown

impl StructuralPartialEq for Unknown