Create custom error type

src/fake.rs

@@ -13,6 +13,9 @@ pub use std::collections::hash_map::{Entry, RandomState};
 
 pub struct HashMap<K, V, S = RandomState>(StdMap<K, V, S>);
 
+
+use FailedAllocationError;
+
 impl<K, V, S> Deref for HashMap<K, V, S> {
     type Target = StdMap<K, V, S>;
     fn deref(&self) -> &Self::Target {
@@ -39,7 +42,7 @@ impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
     }
 
     #[inline]
-    pub fn try_with_capacity(capacity: usize) -> Result<HashMap<K, V, RandomState>, ()> {
+    pub fn try_with_capacity(capacity: usize) -> Result<HashMap<K, V, RandomState>, FailedAllocationError> {
         Ok(HashMap(StdMap::with_capacity(capacity)))
     }
 }
@@ -50,12 +53,12 @@ impl<K, V, S> HashMap<K, V, S>
           S: BuildHasher
 {
     #[inline]
-    pub fn try_with_hasher(hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
+    pub fn try_with_hasher(hash_builder: S) -> Result<HashMap<K, V, S>, FailedAllocationError> {
         Ok(HashMap(StdMap::with_hasher(hash_builder)))
     }
 
     #[inline]
-    pub fn try_with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
+    pub fn try_with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Result<HashMap<K, V, S>, FailedAllocationError> {
         Ok(HashMap(StdMap::with_capacity_and_hasher(capacity, hash_builder)))
     }
 
@@ -65,20 +68,20 @@ impl<K, V, S> HashMap<K, V, S>
 
 
     #[inline]
-    pub fn try_reserve(&mut self, additional: usize) -> Result<(), ()> {
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), FailedAllocationError> {
         Ok(self.reserve(additional))
     }
 
-    pub fn try_shrink_to_fit(&mut self) -> Result<(), ()> {
+    pub fn try_shrink_to_fit(&mut self) -> Result<(), FailedAllocationError> {
         Ok(self.shrink_to_fit())
     }
 
-    pub fn try_entry(&mut self, key: K) -> Result<Entry<K, V>, ()> {
+    pub fn try_entry(&mut self, key: K) -> Result<Entry<K, V>, FailedAllocationError> {
         Ok(self.entry(key))
     }
 
     #[inline]
-    pub fn try_insert(&mut self, k: K, v: V) -> Result<Option<V>, ()> {
+    pub fn try_insert(&mut self, k: K, v: V) -> Result<Option<V>, FailedAllocationError> {
         Ok(self.insert(k, v))
     }
 }
@@ -130,17 +133,17 @@ impl<T, S> HashSet<T, S>
     }
 
     #[inline]
-    pub fn try_reserve(&mut self, additional: usize) -> Result<(), ()> {
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), FailedAllocationError> {
         Ok(self.reserve(additional))
     }
 
     #[inline]
-    pub fn try_shrink_to_fit(&mut self) -> Result<(), ()> {
+    pub fn try_shrink_to_fit(&mut self) -> Result<(), FailedAllocationError> {
         Ok(self.shrink_to_fit())
     }
 
     #[inline]
-    pub fn try_insert(&mut self, value: T) -> Result<bool, ()> {
+    pub fn try_insert(&mut self, value: T) -> Result<bool, FailedAllocationError> {
         Ok(self.insert(value))
     }
 }

src/hash_map.rs

@@ -23,6 +23,8 @@ use ops::{Deref, Index};
 use super::table::{self, Bucket, EmptyBucket, FullBucket, FullBucketMut, RawTable, SafeHash};
 use super::table::BucketState::{Empty, Full};
 
+use FailedAllocationError;
+
 const MIN_NONZERO_RAW_CAPACITY: usize = 32;     // must be a power of two
 
 static OOM_STR: &str = "out of memory whilst allocating hashmap"; 
@@ -614,7 +616,7 @@ impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
     }
 
     #[inline]
-    pub fn try_with_capacity(capacity: usize) -> Result<HashMap<K, V, RandomState>, ()> {
+    pub fn try_with_capacity(capacity: usize) -> Result<HashMap<K, V, RandomState>, FailedAllocationError> {
         HashMap::try_with_capacity_and_hasher(capacity, Default::default())
     }
 }
@@ -644,7 +646,7 @@ impl<K, V, S> HashMap<K, V, S>
     /// map.insert(1, 2);
     /// ```
     #[inline]
-    pub fn try_with_hasher(hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
+    pub fn try_with_hasher(hash_builder: S) -> Result<HashMap<K, V, S>, FailedAllocationError> {
         Ok(HashMap {
             hash_builder,
             resize_policy: DefaultResizePolicy::new(),
@@ -679,7 +681,7 @@ impl<K, V, S> HashMap<K, V, S>
     /// map.insert(1, 2);
     /// ```
     #[inline]
-    pub fn try_with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Result<HashMap<K, V, S>, ()> {
+    pub fn try_with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Result<HashMap<K, V, S>, FailedAllocationError> {
         let resize_policy = DefaultResizePolicy::new();
         let raw_cap = resize_policy.raw_capacity(capacity);
         Ok(HashMap {
@@ -746,7 +748,7 @@ impl<K, V, S> HashMap<K, V, S>
 
 
     #[inline]
-    pub fn try_reserve(&mut self, additional: usize) -> Result<(), ()> {
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), FailedAllocationError> {
         let remaining = self.capacity() - self.len(); // this can't overflow
         if remaining < additional {
             let min_cap = self.len().checked_add(additional).expect("reserve overflow");
@@ -763,7 +765,7 @@ impl<K, V, S> HashMap<K, V, S>
 
     #[cold]
     #[inline(never)]
-    fn try_resize(&mut self, new_raw_cap: usize) -> Result<(), ()> {
+    fn try_resize(&mut self, new_raw_cap: usize) -> Result<(), FailedAllocationError> {
         assert!(self.table.size() <= new_raw_cap);
         assert!(new_raw_cap.is_power_of_two() || new_raw_cap == 0);
 
@@ -829,7 +831,7 @@ impl<K, V, S> HashMap<K, V, S>
         self.try_shrink_to_fit().expect(OOM_STR);
     }
 
-    pub fn try_shrink_to_fit(&mut self) -> Result<(), ()> {
+    pub fn try_shrink_to_fit(&mut self) -> Result<(), FailedAllocationError> {
         let new_raw_cap = self.resize_policy.raw_capacity(self.len());
         if self.raw_capacity() != new_raw_cap {
             let old_table = replace(&mut self.table, RawTable::new(new_raw_cap)?);
@@ -1002,7 +1004,7 @@ impl<K, V, S> HashMap<K, V, S>
         self.try_entry(key).expect(OOM_STR)
     }
 
-    pub fn try_entry(&mut self, key: K) -> Result<Entry<K, V>, ()> {
+    pub fn try_entry(&mut self, key: K) -> Result<Entry<K, V>, FailedAllocationError> {
         // Gotta resize now.
         self.try_reserve(1)?;
         let hash = self.make_hash(&key);
@@ -1195,7 +1197,7 @@ impl<K, V, S> HashMap<K, V, S>
     }
 
     #[inline]
-    pub fn try_insert(&mut self, k: K, v: V) -> Result<Option<V>, ()> {
+    pub fn try_insert(&mut self, k: K, v: V) -> Result<Option<V>, FailedAllocationError> {
         let hash = self.make_hash(&k);
         self.try_reserve(1)?;
         Ok(self.insert_hashed_nocheck(hash, k, v))

src/lib.rs

@@ -8,6 +8,8 @@ pub mod hash_set;
 
 pub mod fake;
 
+use std::{error, fmt};
+
 trait Recover<Q: ?Sized> {
     type Key;
 
@@ -15,3 +17,20 @@ trait Recover<Q: ?Sized> {
     fn take(&mut self, key: &Q) -> Option<Self::Key>;
     fn replace(&mut self, key: Self::Key) -> Option<Self::Key>;
 }
+
+#[derive(Debug)]
+pub struct FailedAllocationError {
+    reason: &'static str,
+}
+
+impl error::Error for FailedAllocationError {
+    fn description(&self) -> &str {
+        self.reason
+    }
+}
+
+impl fmt::Display for FailedAllocationError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.reason.fmt(f)
+    }
+}

src/table.rs

@@ -19,6 +19,7 @@ use ptr;
 use shim::{Unique, Shared};
 
 use self::BucketState::*;
+use FailedAllocationError;
 
 /// Integer type used for stored hash values.
 ///
@@ -728,7 +729,7 @@ impl<K, V> RawTable<K, V> {
 
     /// Does not initialize the buckets. The caller should ensure they,
     /// at the very least, set every hash to EMPTY_BUCKET.
-    unsafe fn try_new_uninitialized(capacity: usize) -> Result<RawTable<K, V>, ()> {
+    unsafe fn try_new_uninitialized(capacity: usize) -> Result<RawTable<K, V>, FailedAllocationError> {
         if capacity == 0 {
             return Ok(RawTable {
                 size: 0,
@@ -757,8 +758,7 @@ impl<K, V> RawTable<K, V> {
                                                                         align_of::<(K, V)>());
 
         if oflo {
-            // capacity overflow
-            return Err(());
+            return Err(FailedAllocationError { reason: "capacity overflow when allocating RawTable" });
         }
 
         // One check for overflow that covers calculation and rounding of size.
@@ -768,12 +768,11 @@ impl<K, V> RawTable<K, V> {
 
         if let Some(cap_bytes) = cap_bytes {
             if size < cap_bytes {
-                // capacity overflow
-                return Err(());
+                return Err(FailedAllocationError { reason: "capacity overflow when allocating RawTable" });
             }
         } else {
-            // capacity overflow
-            return Err(());
+            
+            return Err(FailedAllocationError { reason: "capacity overflow when allocating RawTable" });
         }
 
 
@@ -782,8 +781,8 @@ impl<K, V> RawTable<K, V> {
         let buffer = alloc(size, alignment);
         
         if buffer.is_null() {
-            // OOM
-            return Err(())
+            
+            return Err(FailedAllocationError { reason: "out of memory when allocating RawTable" });
         }
 
         let hashes = buffer.offset(hash_offset as isize) as *mut HashUint;
@@ -817,7 +816,7 @@ impl<K, V> RawTable<K, V> {
 
     /// Creates a new raw table from a given capacity. All buckets are
     /// initially empty.
-    pub fn new(capacity: usize) -> Result<RawTable<K, V>, ()> {
+    pub fn new(capacity: usize) -> Result<RawTable<K, V>, FailedAllocationError> {
         unsafe {
             let ret = RawTable::try_new_uninitialized(capacity)?;
             ptr::write_bytes(ret.hashes.ptr(), 0, capacity);