From 0a8f9ac5c00d50f9075e95d935d2b70be3a64d33 Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@cs.stanford.edu>
Date: Mon, 6 Oct 2025 08:30:34 -0700
Subject: [PATCH] Add `ToSmallString`, analogous to standard `ToString`.

---
 src/string.rs | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/src/string.rs b/src/string.rs
index 5b22c92..78a8bdf 100644
--- a/src/string.rs
+++ b/src/string.rs
@@ -2,7 +2,7 @@ use core::{
     borrow::{Borrow, BorrowMut},
     cmp::Ordering,
     convert::Infallible,
-    fmt,
+    fmt::{self, Display, Write},
     hash::{Hash, Hasher},
     iter::{FromIterator, FusedIterator},
     ops, ptr, slice,
@@ -961,6 +961,43 @@ impl<A: Array<Item = u8>> fmt::Display for FromUtf8Error<A> {
     }
 }
 
+/// A trait for converting a value to a [`SmallString`].
+///
+/// This trait is automatically implemented for any type which implements the
+/// [`Display`] trait.
+pub trait ToSmallString {
+    /// Converts this type to a [`SmallString`], analogous to `.to_string()` for
+    /// converting to a [`String`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use smallstr::{SmallString, ToSmallString};
+    /// // Works with any type that implements `Display`.
+    /// let s = 123.to_small_string::<8>();
+    ///
+    /// // Works for arbitrary formatting with `format_args!`.
+    /// let s: SmallString<[u8; 32]> = format_args!("Hello, {}!", "world").to_small_string();
+    /// ```
+    fn to_small_string<const N: usize>(&self) -> SmallString<[u8; N]>
+    where
+        [u8; N]: Array<Item = u8>;
+}
+
+impl<T> ToSmallString for T
+where
+    T: Display,
+{
+    fn to_small_string<const N: usize>(&self) -> SmallString<[u8; N]>
+    where
+        [u8; N]: Array<Item = u8>,
+    {
+        let mut s = SmallString::new();
+        write!(&mut s, "{self}").unwrap();
+        s
+    }
+}
+
 #[cfg(test)]
 mod test {
     use alloc::{
@@ -969,6 +1006,8 @@ mod test {
         string::{String, ToString},
     };
 
+    use crate::ToSmallString;
+
     use super::SmallString;
 
     #[test]
@@ -1232,6 +1271,15 @@ mod test {
         assert_eq!(s, "foo");
     }
 
+    #[test]
+    fn test_to_small_string() {
+        assert_eq!(123.to_small_string::<8>(), "123");
+        assert_eq!(
+            format_args!("Hello, {}!", "world").to_small_string::<16>(),
+            "Hello, world!"
+        );
+    }
+
     #[cfg(feature = "serde")]
     #[test]
     fn test_serde() {