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use core::fmt;
#[derive(Default, Debug, Clone, Copy)]
enum SizeHintKind {
/// The length isn't known.
#[default]
Any,
/// The length is exactly known.
Exact(usize),
}
/// A length hint.
#[derive(Default, Debug, Clone, Copy)]
#[non_exhaustive]
#[doc(hidden)]
pub struct SizeHint {
kind: SizeHintKind,
}
impl SizeHint {
/// Construct a size hint of unknown size.
///
/// # Examples
///
/// ```
/// use musli::de::SizeHint;
///
/// let hint = SizeHint::any();
/// assert_eq!(hint.or_default(), 0);
/// ```
#[inline]
pub const fn any() -> Self {
SizeHint {
kind: SizeHintKind::Any,
}
}
/// Construct an exactly sized hint.
///
/// # Examples
///
/// ```
/// use musli::de::SizeHint;
///
/// let hint = SizeHint::exact(16);
/// assert_eq!(hint.or_default(), 16);
/// ```
#[inline]
pub const fn exact(length: usize) -> Self {
SizeHint {
kind: SizeHintKind::Exact(length),
}
}
/// Get a size hint or a default value.
///
/// # Examples
///
/// ```
/// use musli::de::SizeHint;
///
/// let hint = SizeHint::any();
/// assert_eq!(hint.or_default(), 0);
/// ```
#[inline]
pub fn or_default(self) -> usize {
match self.kind {
SizeHintKind::Any => 0,
SizeHintKind::Exact(n) => n,
}
}
}
impl From<Option<usize>> for SizeHint {
#[inline]
fn from(value: Option<usize>) -> Self {
let kind = match value {
Some(n) => SizeHintKind::Exact(n),
None => SizeHintKind::Any,
};
SizeHint { kind }
}
}
impl fmt::Display for SizeHint {
#[inline]
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.kind {
SizeHintKind::Any => write!(f, "unknown length"),
SizeHintKind::Exact(length) => write!(f, "size {length}"),
}
}
}
impl SizeHint {
/// Coerce into an `Option`.
#[inline]
pub fn into_option(self) -> Option<usize> {
match self.kind {
SizeHintKind::Any => None,
SizeHintKind::Exact(len) => Some(len),
}
}
}