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authorGravatar Matt Calabrese <calabrese@google.com>2017-10-12 10:09:49 -0700
committerGravatar GitHub <noreply@github.com>2017-10-12 10:09:49 -0700
commit1a9ba5e2e5a14413704f0c913fac53359576d3b6 (patch)
tree4adf57a4eadcfcd1de9dcce2803071a28fa53cfe
parent40b90bcfda2d08c55c1bb347d1780321f5896868 (diff)
parentbbf83057e5f611a66ba9dfeabb14ccfd5cf08ac7 (diff)
Merge pull request #28 from Bronek/constexpr-any-type-id
Make any_internal::FastTypeId() and IdForType() constexpr
-rw-r--r--absl/types/any.h39
1 files changed, 18 insertions, 21 deletions
diff --git a/absl/types/any.h b/absl/types/any.h
index a51dea11..2e7bf21f 100644
--- a/absl/types/any.h
+++ b/absl/types/any.h
@@ -94,23 +94,20 @@ namespace absl {
namespace any_internal {
-// FastTypeId<Type>() evaluates at compile/link-time to a unique integer for the
-// passed in type. Their values are neither contiguous nor small, making them
-// unfit for using as an index into a vector, but a good match for keys into
-// maps or straight up comparisons.
-// Note that on 64-bit (unix) systems size_t is 64-bit while int is 32-bit and
-// the compiler will happily and quietly assign such a 64-bit value to a
-// 32-bit integer. While a client should never do that it SHOULD still be safe,
-// assuming the BSS segment doesn't span more than 4GiB.
+template <typename Type>
+struct TypeTag {
+ constexpr static char dummy_var = 0;
+};
+
+template <typename Type>
+constexpr char TypeTag<Type>::dummy_var;
+
+// FastTypeId<Type>() evaluates at compile/link-time to a unique pointer for the
+// passed in type. These are meant to be good match for keys into maps or
+// straight up comparisons.
template<typename Type>
-inline size_t FastTypeId() {
- static_assert(sizeof(char*) <= sizeof(size_t),
- "ptr size too large for size_t");
-
- // This static variable isn't actually used, only its address, so there are
- // no concurrency issues.
- static char dummy_var;
- return reinterpret_cast<size_t>(&dummy_var);
+constexpr inline const void* FastTypeId() {
+ return &TypeTag<Type>::dummy_var;
}
} // namespace any_internal
@@ -382,7 +379,7 @@ class any {
public:
virtual ~ObjInterface() = default;
virtual std::unique_ptr<ObjInterface> Clone() const = 0;
- virtual size_t type_id() const noexcept = 0;
+ virtual const void* ObjTypeId() const noexcept = 0;
#if ABSL_ANY_DETAIL_HAS_RTTI
virtual const std::type_info& Type() const noexcept = 0;
#endif // ABSL_ANY_DETAIL_HAS_RTTI
@@ -400,7 +397,7 @@ class any {
return std::unique_ptr<ObjInterface>(new Obj(in_place, value));
}
- size_t type_id() const noexcept final { return IdForType<T>(); }
+ const void* ObjTypeId() const noexcept final { return IdForType<T>(); }
#if ABSL_ANY_DETAIL_HAS_RTTI
const std::type_info& Type() const noexcept final { return typeid(T); }
@@ -415,7 +412,7 @@ class any {
}
template <typename T>
- static size_t IdForType() {
+ constexpr static const void* IdForType() {
// Note: This type dance is to make the behavior consistent with typeid.
using NormalizedType =
typename std::remove_cv<typename std::remove_reference<T>::type>::type;
@@ -423,8 +420,8 @@ class any {
return any_internal::FastTypeId<NormalizedType>();
}
- size_t GetObjTypeId() const {
- return obj_ == nullptr ? any_internal::FastTypeId<void>() : obj_->type_id();
+ const void* GetObjTypeId() const {
+ return obj_ ? obj_->ObjTypeId() : any_internal::FastTypeId<void>();
}
// `absl::any` nonmember functions //