Trait FmtEq 

pub trait FmtEq: Display + Eq { }

A marker trait for types whose equivalence relation is the same as equivalence between its Display representation.

When T implements FmtEq, the following property must be upheld for all a: T and b: T:

assert_eq!(a == b, *format!("{}", a) == *format!("{}", b));

In other words (assuming that no ill-defined specialization is involved):

a == b <-> a.to_string() == b.to_string()

Corollaries

From str: Eq and the above property, it follows that T satisfies Eq trait’s contract, i.e., reflexivity, symmetricity and transitivity of == operator.

Examples

Floating-point number primitives do not satisfy the property (they are not even Eq):

assert_eq!(0.0, -0.0);
assert_ne!(0.0.to_string(), (-0.0).to_string());

assert_ne!(f64::NAN, f64::NAN);
assert_eq!(f64::NAN.to_string(), f64::NAN.to_string());

Wrapping any Display type with fmt_cmp::Cmp makes it FmtEq:

assert_ne!(fmt_cmp::Cmp(0.0), fmt_cmp::Cmp(-0.0));
assert_eq!(fmt_cmp::Cmp(f64::NAN), fmt_cmp::Cmp(f64::NAN));

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl FmtEq for Infallible

impl FmtEq for bool

impl FmtEq for i8

impl FmtEq for i16

impl FmtEq for i32

impl FmtEq for i64

impl FmtEq for i128

impl FmtEq for isize

impl FmtEq for str

impl FmtEq for u8

impl FmtEq for u16

impl FmtEq for u32

impl FmtEq for u64

impl FmtEq for u128

impl FmtEq for usize

impl FmtEq for String

Available on crate feature alloc only.

impl<P: Borrow<<P as Deref>::Target> + Deref + Display> FmtEq for Pin<P>

where P::Target: FmtEq,

impl<T: FmtEq + ToOwned + ?Sized> FmtEq for Cow<'_, T>

where T::Owned: Display,

Available on crate feature alloc only.

impl<T: FmtEq + ?Sized> FmtEq for &T

impl<T: FmtEq + ?Sized> FmtEq for &mut T

impl<T: FmtEq + ?Sized> FmtEq for Box<T>

Available on crate feature alloc only.

impl<T: FmtEq + ?Sized> FmtEq for Rc<T>

Available on crate feature alloc only.

impl<T: FmtEq + ?Sized> FmtEq for Arc<T>

Available on crate feature alloc only.

Implementors

impl<T: Display + ?Sized> FmtEq for Cmp<T>