Trait const_panic::fmt::PanicFmt
source · pub trait PanicFmt {
type This: ?Sized;
type Kind;
const PV_COUNT: usize;
const PROOF: IsPanicFmt<Self, Self::This, Self::Kind> = IsPanicFmt::NEW;
}Expand description
Trait for types that can be formatted by const panics.
Implementor
Implementors are expected to also define this inherent method to format the type:
const fn to_panicvals<'a>(&'a self, f: FmtArg) -> [PanicVal<'a>; <Self as PanicFmt>::PV_COUNT]The returned PanicVal can also be PanicVal<'static>.
Implementation examples
This trait can be implemented in these ways (in increasing order of verbosity):
- Using the
PanicFmtderive macro (requires the opt-in"derive"feature) - Using the
impl_panicfmtmacro (requires the default-enabled"non_basic"feature) - Using the
flatten_panicvalsmacro (requires the default-enabled"non_basic"feature) - Using no macros at all
Macro-less impl
Implementing this trait for a simple enum without using macros.
ⓘ
use const_panic::{ArrayString, FmtArg, PanicFmt, PanicVal};
// `ArrayString` requires the "non_basic" crate feature (enabled by default),
// everything else in this example works with no enabled crate features.
assert_eq!(
ArrayString::<99>::concat_panicvals(&[
&Foo::Bar.to_panicvals(FmtArg::DEBUG),
&[PanicVal::write_str(",")],
&Foo::Baz.to_panicvals(FmtArg::DEBUG),
&[PanicVal::write_str(",")],
&Foo::Qux.to_panicvals(FmtArg::DEBUG),
]).unwrap(),
"Bar,Baz,Qux",
);
enum Foo {
Bar,
Baz,
Qux,
}
impl PanicFmt for Foo {
type This = Self;
type Kind = const_panic::IsCustomType;
const PV_COUNT: usize = 1;
}
impl Foo {
pub const fn to_panicvals(self, _: FmtArg) -> [PanicVal<'static>; Foo::PV_COUNT] {
match self {
Self::Bar => [PanicVal::write_str("Bar")],
Self::Baz => [PanicVal::write_str("Baz")],
Self::Qux => [PanicVal::write_str("Qux")],
}
}
}
Required Associated Types§
sourcetype This: ?Sized
type This: ?Sized
The type after dereferencing all references.
User-defined types should generally set this to Self.
sourcetype Kind
type Kind
Whether this is a user-defined type or standard library type.
User-defined types should generally set this to IsCustomType.
Required Associated Constants§
Provided Associated Constants§
sourceconst PROOF: IsPanicFmt<Self, Self::This, Self::Kind> = IsPanicFmt::NEW
const PROOF: IsPanicFmt<Self, Self::This, Self::Kind> = IsPanicFmt::NEW
A marker type that proves that Self implements PanicFmt.
Used by const_panic macros to coerce both standard library and
user-defined types into some type that has a to_panicvals method.
Object Safety§
This trait is not object safe.