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use std::fmt;
/// Debug-formats the given slice, but only up to the first `max_len` elements.
/// Any further elements are replaced by an ellipsis.
///
/// See also [`slice_truncated()`],
pub struct TruncatedSlice<'a, T> {
inner: &'a [T],
max_len: usize,
}
impl<T: fmt::Debug> fmt::Debug for TruncatedSlice<'_, T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if self.inner.len() <= self.max_len {
write!(f, "{:?}", self.inner)
} else {
f.debug_list()
.entries(&self.inner[..self.max_len])
.entry(&"...")
.finish()
}
}
}
/// See [`TruncatedSlice`]. Useful for `#[instrument]`:
///
/// ```
/// use conduit_core::utils::debug::slice_truncated;
///
/// #[tracing::instrument(fields(foos = slice_truncated(foos, 42)))]
/// fn bar(foos: &[&str]);
/// ```
pub fn slice_truncated<T: fmt::Debug>(
slice: &[T], max_len: usize,
) -> tracing::field::DebugValue<TruncatedSlice<'_, T>> {
tracing::field::debug(TruncatedSlice {
inner: slice,
max_len,
})
}