feat: add function create new MultiVec with capacity

1 files changed, 20 insertions, 4 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 698e641..228b7e1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -70,6 +70,22 @@ where
         }
     }
 
+    pub fn with_capacity(capacity: usize) -> Self
+    {
+        let mut this = Self {
+            _pd: PhantomData,
+            ptr: NonNull::dangling(),
+            field_arr_byte_offsets: Vec::new(),
+            length: 0,
+            capacity: 0,
+            layout: None,
+        };
+
+        this.do_first_alloc(capacity);
+
+        this
+    }
+
     /// Pushes a item to the `MultiVec`.
     ///
     /// ## Note on performance
@@ -90,7 +106,7 @@ where
             return;
         }
 
-        self.do_first_alloc();
+        self.do_first_alloc(1);
 
         self.write_item(0, item);
 
@@ -184,16 +200,16 @@ where
         self.field_arr_byte_offsets = new_field_arr_byte_offsets;
     }
 
-    fn do_first_alloc(&mut self)
+    fn do_first_alloc(&mut self, capacity: usize)
     {
-        let (layout, field_arr_byte_offsets) = Self::create_layout(1);
+        let (layout, field_arr_byte_offsets) = Self::create_layout(capacity);
 
         let Some(ptr) = NonNull::new(unsafe { alloc(layout) }) else {
             handle_alloc_error(layout);
         };
 
         self.ptr = ptr;
-        self.capacity = 1;
+        self.capacity = capacity;
         self.field_arr_byte_offsets = field_arr_byte_offsets;
         self.layout = Some(layout);
     }