Consider template args for default constructor noexceptness

This adds a helper to detect the default growth policies that are noexcept when default initialized with 0.
Tessil · Aug 27, 2024 · 33f41b2 · 33f41b2
1 parent 2b7dd4a
commit 33f41b2
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Showing 5 changed files with 41 additions and 4 deletions.
diff --git a/include/tsl/bhopscotch_map.h b/include/tsl/bhopscotch_map.h
@@ -119,7 +119,13 @@ class bhopscotch_map {
   /*
    * Constructors
    */
-  bhopscotch_map() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0) : bhopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
+  bhopscotch_map() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
+                            std::is_nothrow_default_constructible<Hash>::value &&
+                            std::is_nothrow_default_constructible<KeyEqual>::value &&
+                            std::is_nothrow_default_constructible<Allocator>::value &&
+                            (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
+                             hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
+      : bhopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
 
   explicit bhopscotch_map(size_type bucket_count, const Hash& hash = Hash(),
                           const KeyEqual& equal = KeyEqual(),

diff --git a/include/tsl/bhopscotch_set.h b/include/tsl/bhopscotch_set.h
@@ -102,7 +102,13 @@ class bhopscotch_set {
   /*
    * Constructors
    */
-  bhopscotch_set() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0) : bhopscotch_set(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
+  bhopscotch_set() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
+                            std::is_nothrow_default_constructible<Hash>::value &&
+                            std::is_nothrow_default_constructible<KeyEqual>::value &&
+                            std::is_nothrow_default_constructible<Allocator>::value &&
+                            (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
+                             hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
+      : bhopscotch_set(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
 
   explicit bhopscotch_set(size_type bucket_count, const Hash& hash = Hash(),
                           const KeyEqual& equal = KeyEqual(),

diff --git a/include/tsl/hopscotch_growth_policy.h b/include/tsl/hopscotch_growth_policy.h
@@ -399,6 +399,19 @@ class prime_growth_policy {
                 "The type of m_iprime is not big enough.");
 };
 
+/**
+ * SFINAE helper to detect growth policies which can be noexcept-initialized
+ * with a zero min bucket count.
+ */
+template<typename>
+struct is_noexcept_on_zero_init : std::false_type {};
+template<std::size_t GrowthFactor>
+struct is_noexcept_on_zero_init<power_of_two_growth_policy<GrowthFactor>> : std::true_type {};
+template<class GrowthFactor>
+struct is_noexcept_on_zero_init<mod_growth_policy<GrowthFactor>> : std::true_type {};
+template<>
+struct is_noexcept_on_zero_init<prime_growth_policy> : std::true_type {};
+
 }  // namespace hh
 }  // namespace tsl
 

diff --git a/include/tsl/hopscotch_map.h b/include/tsl/hopscotch_map.h
@@ -135,7 +135,13 @@ class hopscotch_map {
   /*
    * Constructors
    */
-  hopscotch_map() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0) : hopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
+  hopscotch_map() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
+                           std::is_nothrow_default_constructible<Hash>::value &&
+                           std::is_nothrow_default_constructible<KeyEqual>::value &&
+                           std::is_nothrow_default_constructible<Allocator>::value &&
+                           (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
+                            hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
+      : hopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
 
   explicit hopscotch_map(size_type bucket_count, const Hash& hash = Hash(),
                          const KeyEqual& equal = KeyEqual(),

diff --git a/include/tsl/hopscotch_set.h b/include/tsl/hopscotch_set.h
@@ -123,7 +123,13 @@ class hopscotch_set {
   /*
    * Constructors
    */
-  hopscotch_set() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0) : hopscotch_set(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
+  hopscotch_set() noexcept(ht::DEFAULT_INIT_BUCKETS_SIZE == 0 &&
+                           std::is_nothrow_default_constructible<Hash>::value &&
+                           std::is_nothrow_default_constructible<KeyEqual>::value &&
+                           std::is_nothrow_default_constructible<Allocator>::value &&
+                           (std::is_nothrow_constructible<GrowthPolicy, std::size_t&>::value ||
+                            hh::is_noexcept_on_zero_init<GrowthPolicy>::value))
+      : hopscotch_set(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
 
   explicit hopscotch_set(size_type bucket_count, const Hash& hash = Hash(),
                          const KeyEqual& equal = KeyEqual(),