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use std::u64;
/// A `Body` size hint
///
/// The default implementation returns:
///
/// * 0 for `lower`
/// * `None` for `upper`.
#[derive(Debug, Default, Clone)]
pub struct SizeHint {
lower: u64,
upper: Option<u64>,
}
impl SizeHint {
/// Returns a new `SizeHint` with default values
#[inline]
pub fn new() -> SizeHint {
SizeHint::default()
}
/// Returns a new `SizeHint` with both upper and lower bounds set to the
/// given value.
#[inline]
pub fn with_exact(value: u64) -> SizeHint {
SizeHint {
lower: value,
upper: Some(value),
}
}
/// Returns the lower bound of data that the `Body` will yield before
/// completing.
#[inline]
pub fn lower(&self) -> u64 {
self.lower
}
/// Set the value of the `lower` hint.
///
/// # Panics
///
/// The function panics if `value` is greater than `upper`.
#[inline]
pub fn set_lower(&mut self, value: u64) {
assert!(value <= self.upper.unwrap_or(u64::MAX));
self.lower = value;
}
/// Returns the upper bound of data the `Body` will yield before
/// completing, or `None` if the value is unknown.
#[inline]
pub fn upper(&self) -> Option<u64> {
self.upper
}
/// Set the value of the `upper` hint value.
///
/// # Panics
///
/// This function panics if `value` is less than `lower`.
#[inline]
pub fn set_upper(&mut self, value: u64) {
assert!(value >= self.lower, "`value` is less than than `lower`");
self.upper = Some(value);
}
/// Returns the exact size of data that will be yielded **if** the
/// `lower` and `upper` bounds are equal.
#[inline]
pub fn exact(&self) -> Option<u64> {
if Some(self.lower) == self.upper {
self.upper
} else {
None
}
}
/// Set the value of the `lower` and `upper` bounds to exactly the same.
#[inline]
pub fn set_exact(&mut self, value: u64) {
self.lower = value;
self.upper = Some(value);
}
}