Make Vec::new const

[rust.git] / src / liballoc / raw_vec.rs

diff --git a/src/liballoc/raw_vec.rs b/src/liballoc/raw_vec.rs
index 24b7cd3db0cc67e27569fcc4bf821f808abee812..dc8ad9ee06169279fafa461a96769a32593f04c7 100644 (file)
--- a/src/liballoc/raw_vec.rs
+++ b/src/liballoc/raw_vec.rs
@@ -14,7 +14,7 @@
 use core::ptr::{self, NonNull, Unique};
 use core::slice;
 
-use alloc::{Alloc, Layout, Global};
+use alloc::{Alloc, Layout, Global, oom};
 use alloc::CollectionAllocErr;
 use alloc::CollectionAllocErr::*;
 use boxed::Box;
@@ -68,6 +68,16 @@ pub fn new_in(a: A) -> Self {
         }
     }
 
+    /// Like `empty` but parametrized over the choice of allocator for the returned `RawVec`.
+    pub const fn empty_in(a: A) -> Self {
+        // Unique::empty() doubles as "unallocated" and "zero-sized allocation"
+        RawVec {
+            ptr: Unique::empty(),
+            cap: 0,
+            a,
+        }
+    }
+
     /// Like `with_capacity` but parameterized over the choice of
     /// allocator for the returned RawVec.
     #[inline]
@@ -101,7 +111,7 @@ fn allocate_in(cap: usize, zeroed: bool, mut a: A) -> Self {
                 };
                 match result {
                     Ok(ptr) => ptr,
-                    Err(_) => a.oom(),
+                    Err(_) => oom(),
                 }
             };
 
@@ -124,6 +134,12 @@ pub fn new() -> Self {
         Self::new_in(Global)
     }
 
+    /// Create a `RawVec` with capcity 0 (on the system heap), regardless of `T`, without
+    /// allocating.
+    pub fn empty() -> Self {
+        Self::empty_in(Global)
+    }
+
     /// Creates a RawVec (on the system heap) with exactly the
     /// capacity and alignment requirements for a `[T; cap]`. This is
     /// equivalent to calling RawVec::new when `cap` is 0 or T is
@@ -316,7 +332,7 @@ pub fn double(&mut self) {
                                                  new_size);
                     match ptr_res {
                         Ok(ptr) => (new_cap, ptr.cast().into()),
-                        Err(_) => self.a.oom(),
+                        Err(_) => oom(),
                     }
                 }
                 None => {
@@ -325,7 +341,7 @@ pub fn double(&mut self) {
                     let new_cap = if elem_size > (!0) / 8 { 1 } else { 4 };
                     match self.a.alloc_array::<T>(new_cap) {
                         Ok(ptr) => (new_cap, ptr.into()),
-                        Err(_) => self.a.oom(),
+                        Err(_) => oom(),
                     }
                 }
             };
@@ -442,7 +458,7 @@ pub fn try_reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize)
     pub fn reserve_exact(&mut self, used_cap: usize, needed_extra_cap: usize) {
         match self.try_reserve_exact(used_cap, needed_extra_cap) {
             Err(CapacityOverflow) => capacity_overflow(),
-            Err(AllocErr) => self.a.oom(),
+            Err(AllocErr) => oom(),
             Ok(()) => { /* yay */ }
          }
      }
@@ -552,7 +568,7 @@ pub fn try_reserve(&mut self, used_cap: usize, needed_extra_cap: usize)
     pub fn reserve(&mut self, used_cap: usize, needed_extra_cap: usize) {
         match self.try_reserve(used_cap, needed_extra_cap) {
             Err(CapacityOverflow) => capacity_overflow(),
-            Err(AllocErr) => self.a.oom(),
+            Err(AllocErr) => oom(),
             Ok(()) => { /* yay */ }
          }
      }
@@ -667,7 +683,7 @@ pub fn shrink_to_fit(&mut self, amount: usize) {
                                      old_layout,
                                      new_size) {
                     Ok(p) => self.ptr = p.cast().into(),
-                    Err(_) => self.a.oom(),
+                    Err(_) => oom(),
                 }
             }
             self.cap = amount;