add truncate method and tests based on the Vec examples

src/lib.rs

@@ -5,6 +5,7 @@
 
 use core::ops::{Deref, DerefMut};
 use core::mem::replace;
+use core::mem::needs_drop;
 
 extern crate alloc;
 use alloc::vec::Vec;
@@ -113,4 +114,22 @@ impl<T: Default> TinyVec<T> {
       }
     }
   }
+
+  pub fn truncate(&mut self, new_len: usize) {
+    match &mut self.0 {
+      Payload::Inline { len, data } => {
+        if needs_drop::<T>() {
+          while *len > new_len {
+            replace(&mut data[*len - 1], T::default());
+            *len -= 1;
+          }
+        } else {
+          *len = (*len).min(new_len);
+        }
+      }
+      Payload::Heap(ref mut vec) => {
+        vec.truncate(new_len)
+      }
+    }
+  }
 }

tests/basic.rs

@@ -1,10 +1,11 @@
-
-extern crate std;
+#![allow(bad_style)]
 
 use tinyvec::*;
 
+use core::ops::Deref;
+
 #[test]
-fn test_push_pop() {
+fn TinyVec_push_pop() {
   let mut tv = TinyVec::new();
 
   assert_eq!(tv.pop(), None);
@@ -31,3 +32,32 @@ fn test_push_pop() {
   assert_eq!(tv.pop(), None);
   assert_eq!(tv.pop(), None);
 }
+
+#[test]
+fn TinyVec_truncate() {
+  // Truncating a five element vector to two elements
+  let mut tv = TinyVec::new();
+  tv.push(1_i32);
+  tv.push(2);
+  tv.push(3);
+  tv.push(4);
+  tv.push(5);
+  tv.truncate(2);
+  assert_eq!(tv.deref(), [1, 2]);
+
+  // No truncation occurs when len is greater than the vector's current length
+  let mut tv = TinyVec::new();
+  tv.push(1_i32);
+  tv.push(2);
+  tv.push(3);
+  tv.truncate(8);
+  assert_eq!(tv.deref(), [1, 2, 3]);
+
+  // Truncating when len == 0 is equivalent to calling the clear method.
+  let mut tv = TinyVec::new();
+  tv.push(1_i32);
+  tv.push(2);
+  tv.push(3);
+  tv.truncate(0);
+  assert_eq!(tv.deref(), []);
+}