Created
January 25, 2019 15:08
Error: The LazyValue<T> class object must not construct an object of type T when it is created
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#include "test_runner.h" | |
#include <functional> | |
using namespace std; | |
template<typename T> | |
class LazyValue { | |
public: | |
explicit LazyValue(std::function<T()> init) { | |
initializer = move(init); | |
initialized = false; | |
} | |
bool HasValue() const { | |
return initialized; | |
} | |
const T &Get() const { | |
if (!initialized) { | |
value = initializer(); | |
initialized = true; | |
} | |
return value; | |
} | |
private: | |
mutable T value; | |
mutable bool initialized; | |
std::function<T()> initializer; | |
}; | |
void UseExample() { | |
const string big_string = "Giant amounts of memory"; | |
LazyValue<string> lazy_string([&big_string] { return big_string; }); | |
ASSERT(!lazy_string.HasValue()); | |
ASSERT_EQUAL(lazy_string.Get(), big_string); | |
ASSERT_EQUAL(lazy_string.Get(), big_string); | |
} | |
void TestInitializerIsntCalled() { | |
bool called = false; | |
{ | |
LazyValue<int> lazy_int([&called] { | |
called = true; | |
return 0; | |
}); | |
} | |
ASSERT(!called); | |
} | |
int main() { | |
TestRunner tr; | |
RUN_TEST(tr, UseExample); | |
RUN_TEST(tr, TestInitializerIsntCalled); | |
return 0; | |
} |
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