truncate_slice_debug/
lib.rs

1#![doc = include_str!("../README.md")]
2
3use std::fmt;
4
5pub struct TruncatedSlice<'a, T> {
6    max_len: usize,
7    inner: &'a [T],
8}
9
10impl<'a, T> TruncatedSlice<'a, T> {
11    pub fn new(wrapped: &'a [T], max_len: usize) -> Self {
12        Self {
13            max_len,
14            inner: wrapped,
15        }
16    }
17}
18
19impl<'a, T> fmt::Debug for TruncatedSlice<'a, T>
20where
21    T: fmt::Debug,
22{
23    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
24        let dbg_len = std::cmp::min(self.inner.len(), self.max_len);
25        let is_truncated = dbg_len < self.inner.len();
26
27        f.write_str("[")?;
28        for (i, entry) in self.inner[..dbg_len].iter().enumerate() {
29            f.write_fmt(format_args!("{:?}", &entry))?;
30            if i != dbg_len - 1 {
31                f.write_str(", ")?;
32            }
33        }
34
35        if is_truncated {
36            f.write_fmt(format_args!(", ...({} more)", self.inner.len() - dbg_len))?;
37        }
38
39        f.write_str("]")
40    }
41}
42
43pub trait TruncateSliceDebug<'a, T>
44where
45    T: fmt::Debug,
46{
47    /// For a collection of `T`, return a `TruncatedSlice` struct with a `Debug`
48    /// implementation to only print `max_len` items
49    fn truncate_debug(&self, max_len: usize) -> TruncatedSlice<'a, T>;
50}
51
52impl<'a, T> TruncateSliceDebug<'a, T> for &'a [T]
53where
54    T: fmt::Debug,
55{
56    /// `TruncateSliceDebug` implmenetation for any slice of items that implement `Debug`
57    ///
58    /// ```
59    /// use truncate_slice_debug::TruncateSliceDebug;
60    ///
61    /// let values = vec![0, 1, 2, 3, 4, 5];
62    ///
63    /// let dbg_output = format!("{:?}", values.as_slice().truncate_debug(3));
64    /// assert_eq!(&dbg_output, "[0, 1, 2, ...(3 more)]");
65    ///
66    /// let dbg_output = format!("{:?}", values.as_slice().truncate_debug(10));
67    /// assert_eq!(&dbg_output, "[0, 1, 2, 3, 4, 5]");
68    /// ```
69    fn truncate_debug(&self, max_len: usize) -> TruncatedSlice<'a, T> {
70        TruncatedSlice::new(self, max_len)
71    }
72}
73
74#[test]
75fn test_truncated_slice() {
76    let values = vec![7; 10];
77
78    let dbg10 = format!("{:?}", TruncatedSlice::new(&values, 5));
79    assert_eq!(&dbg10, "[7, 7, 7, 7, 7, ...(5 more)]");
80
81    let dbg10 = format!("{:?}", TruncatedSlice::new(&values, 20));
82    assert_eq!(&dbg10, "[7, 7, 7, 7, 7, 7, 7, 7, 7, 7]");
83}
truncate_slice_debug/lib.rs

truncate_slice_debug/
lib.rs
