tpnote_lib/
clone_ext.rs

1//! Extension trait adding a `shallow_clone()` method to `Cow`.
2use std::borrow::Cow;
3
4pub trait CloneExt<'b> {
5    /// Clone a `Cow` without memory allocation.
6    /// Note, the original must outlive the clone! Use case:
7    /// ```no_run
8    /// use crate::tpnote_lib::clone_ext::CloneExt;
9    /// use std::borrow::Cow;
10    /// fn do_something_or_nothing(v: Cow<str>) -> Cow<str> {
11    ///     if v.len() > 3 {
12    ///         let s = "Hello ".to_string() + &*v;
13    ///         Cow::Owned(s)
14    ///     } else {
15    ///         v
16    ///     }
17    /// }
18    ///
19    /// // Sometimes, we only have a `&Cow`, but we need a `Cow`!
20    /// let a: &Cow<str> = &Cow::Owned("world!".to_string());
21    /// let b: Cow<str>  = a.shallow_clone();
22    /// assert_eq!(do_something_or_nothing(b), "Hello world!");
23    ///
24    /// let a: &Cow<str> = &Cow::Owned("ld!".to_string());
25    /// let b: Cow<str>  = a.shallow_clone();
26    /// assert_eq!(do_something_or_nothing(b), "ld!");
27    /// ```
28    fn shallow_clone(&'b self) -> Cow<'b, str>;
29}
30
31impl<'b> CloneExt<'b> for Cow<'b, str> {
32    fn shallow_clone(&'b self) -> Cow<'b, str> {
33        // match *self {
34        //     Self::Borrowed(b) => Self::Borrowed(b),
35        //     Self::Owned(ref o) => Self::Borrowed(o.as_ref()),
36        // }
37        // // This is equivalent to:
38        Cow::Borrowed(&**self)
39    }
40}
tpnote_lib/clone_ext.rs

tpnote_lib/
clone_ext.rs
