Commit 622fe822 authored by Marcelo Juchem's avatar Marcelo Juchem Committed by Jordan DeLong

Implementing a traits class to check for incomplete types

Summary: A traits class to check for incomplete types

Test Plan: unit tests added

Reviewed By: delong.j@fb.com

FB internal diff: D760676
parent ee31dcdd
......@@ -277,6 +277,34 @@ struct IsOneOf<T, T1, Ts...> {
enum { value = std::is_same<T, T1>::value || IsOneOf<T, Ts...>::value };
};
/**
* A traits class to check for incomplete types.
*
* Example:
*
* struct FullyDeclared {}; // complete type
* struct ForwardDeclared; // incomplete type
*
* is_complete<int>::value // evaluates to true
* is_complete<FullyDeclared>::value // evaluates to true
* is_complete<ForwardDeclared>::value // evaluates to false
*
* struct ForwardDeclared {}; // declared, at last
*
* is_complete<ForwardDeclared>::value // now it evaluates to true
*
* @author: Marcelo Juchem <marcelo@fb.com>
*/
template <typename T>
class is_complete {
template <unsigned long long> struct sfinae {};
template <typename U>
constexpr static bool test(sfinae<sizeof(U)>*) { return true; }
template <typename> constexpr static bool test(...) { return false; }
public:
constexpr static bool value = test<T>(nullptr);
};
/*
* Complementary type traits to check for a negative/non-positive value.
*
......
......@@ -96,6 +96,14 @@ TEST(Traits, is_negative) {
EXPECT_FALSE(folly::is_non_positive(1u));
}
struct CompleteType {};
struct IncompleteType;
TEST(Traits, is_complete) {
EXPECT_TRUE((folly::is_complete<int>::value));
EXPECT_TRUE((folly::is_complete<CompleteType>::value));
EXPECT_FALSE((folly::is_complete<IncompleteType>::value));
}
int main(int argc, char ** argv) {
testing::InitGoogleTest(&argc, argv);
google::ParseCommandLineFlags(&argc, &argv, true);
......
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