From 589c60492b6ff11a1256b80e7b22dced33126559 Mon Sep 17 00:00:00 2001
From: Jorge Polanco <55784702+Jorge-Polanco-Roque@users.noreply.github.com>
Date: Sat, 29 Aug 2026 17:42:30 -0600
Subject: [PATCH] Add try_with_capacity fallible constructor

Fallible analogue to with_capacity, mirroring the existing try_reserve
path (uses try_grow, returns Result<Self, CollectionAllocErr>).

Fixes #416

Signed-off-by: Jorge Polanco <55784702+Jorge-Polanco-Roque@users.noreply.github.com>
---
 src/lib.rs    | 13 +++++++++++++
 tests/main.rs | 13 +++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 9aa7009..f5f000f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -849,6 +849,19 @@ impl<T, const N: usize> SmallVec<T, N> {
         this
     }
 
+    /// Constructs a new, empty `SmallVec` with at least the specified capacity,
+    /// returning an error if the allocation fails.
+    ///
+    /// This is the fallible version of [`with_capacity`](Self::with_capacity).
+    #[inline]
+    pub fn try_with_capacity(capacity: usize) -> Result<Self, CollectionAllocErr> {
+        let mut this = Self::new();
+        if capacity > Self::inline_size() {
+            this.try_grow(capacity)?;
+        }
+        Ok(this)
+    }
+
     #[inline]
     pub const fn from_buf<const S: usize>(elements: [T; S]) -> Self {
         const {
diff --git a/tests/main.rs b/tests/main.rs
index a1a0508..3d9745b 100644
--- a/tests/main.rs
+++ b/tests/main.rs
@@ -125,6 +125,19 @@ fn test_with_capacity() {
     assert_eq!(v.capacity(), 10);
 }
 
+#[test]
+fn test_try_with_capacity() {
+    let v: SmallVec<u8, 3> = SmallVec::try_with_capacity(1).unwrap();
+    assert!(v.is_empty());
+    assert!(!v.spilled());
+    assert_eq!(v.capacity(), 3);
+
+    let v: SmallVec<u8, 3> = SmallVec::try_with_capacity(10).unwrap();
+    assert!(v.is_empty());
+    assert!(v.spilled());
+    assert_eq!(v.capacity(), 10);
+}
+
 #[test]
 fn drain() {
     let mut v: SmallVec<u8, 2> = SmallVec::new();