enumflags2/
fallible.rs

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1use super::BitFlag;
2use super::BitFlags;
3use core::convert::TryFrom;
4use core::fmt;
5
6// Coherence doesn't let us use a generic type here. Work around by implementing
7// for each integer type manually.
8for_each_uint! { $ty $hide_docs =>
9    impl<T> TryFrom<$ty> for BitFlags<T>
10    where
11        T: BitFlag<Numeric=$ty>,
12    {
13        type Error = FromBitsError<T>;
14
15        fn try_from(bits: T::Numeric) -> Result<Self, Self::Error> {
16            Self::from_bits(bits)
17        }
18    }
19}
20
21/// The error struct used by [`BitFlags::from_bits`]
22/// and the [`TryFrom`] implementation for invalid values.
23///
24/// Note that the implementation of [`std::error::Error`]
25/// for this type is gated on the `std` feature flag.
26///
27/// ```
28/// # use std::convert::TryInto;
29/// # use enumflags2::{bitflags, BitFlags};
30/// #[bitflags]
31/// #[derive(Clone, Copy, Debug)]
32/// #[repr(u8)]
33/// enum MyFlags {
34///     A = 0b0001,
35///     B = 0b0010,
36///     C = 0b0100,
37///     D = 0b1000,
38/// }
39///
40/// let result: Result<BitFlags<MyFlags>, _> = 0b10101u8.try_into();
41/// assert!(result.is_err());
42/// let error = result.unwrap_err();
43/// assert_eq!(error.truncate(), MyFlags::C | MyFlags::A);
44/// assert_eq!(error.invalid_bits(), 0b10000);
45/// ```
46#[derive(Debug, Copy, Clone)]
47pub struct FromBitsError<T: BitFlag> {
48    pub(crate) flags: BitFlags<T>,
49    pub(crate) invalid: T::Numeric,
50}
51
52impl<T: BitFlag> FromBitsError<T> {
53    /// Return the truncated result of the conversion.
54    pub fn truncate(self) -> BitFlags<T> {
55        self.flags
56    }
57
58    /// Return the bits that didn't correspond to any flags.
59    pub fn invalid_bits(self) -> T::Numeric {
60        self.invalid
61    }
62}
63
64impl<T: BitFlag + fmt::Debug> fmt::Display for FromBitsError<T> {
65    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
66        write!(
67            fmt,
68            "Invalid bits for {:?}: {:#b}",
69            self.flags, self.invalid
70        )
71    }
72}
73
74#[cfg(feature = "std")]
75impl<T: BitFlag + fmt::Debug> std::error::Error for FromBitsError<T> {
76    fn description(&self) -> &str {
77        "invalid bitflags representation"
78    }
79}
enumflags2/fallible.rs

enumflags2/
fallible.rs
