if(n == 0) return 0;

if(n == 1) return 1;

std::size_t a = 0, b = 1, c;

for(; n > 1; --n) {

c = a + b;

a = b;

b = c;

}

return b;

bool theTruth;

bool getTruth() const {

return theTruth;

};

void setTruth(bool newTruth) {

theTruth = newTruth;

}

int i = 0;

auto f = once( [&i](){ ++i; } );

ASSERT_EQ(0, i);

f();

EXPECT_EQ(1, i);

EXPECT_NO_THROW(f());

EXPECT_EQ(1, i);

int i = 0;

auto f = once( [&i](){ ++i; }, 30);

ASSERT_EQ(0, i);

for(int j = 1; j <= 30; ++j) {

f();

EXPECT_EQ(j, i);

}

EXPECT_NO_THROW(f());

EXPECT_EQ(30, i);

int i = 10;

auto f = once( [&i](){ return i; }, 2);

ASSERT_EQ(10, i);

EXPECT_EQ(10, f());

i = 13;

EXPECT_EQ(13, f());

EXPECT_THROW(f(), out_of_calls);

auto s = string{"Hi there!"};

auto f = once( [](){ return string{"Hi there!"}; } );

EXPECT_EQ(s, f());

EXPECT_THROW(f(), out_of_calls);

auto f = once( [](int i, string s){ return to_string(i) + " " + s; }, 2);

EXPECT_EQ("1 time", f(1, "time"));

EXPECT_EQ("2 times", f(2, "times"));

EXPECT_THROW(f(3, "times"), out_of_calls);

auto f = once( multiplies<float>(), 3);

EXPECT_FLOAT_EQ(120.0, f(2.4, 50.0));

EXPECT_FLOAT_EQ(16.5, f(0.5, 33.0));

EXPECT_FLOAT_EQ(145.64, f(11., 13.24));

EXPECT_THROW(f(1.0, 1.0), out_of_calls);

auto f = once( fibonacci, 30 );

for(int i = 0; i < 30; ++i)

EXPECT_EQ(fibonacci(i), f(i));

EXPECT_THROW(f(0), out_of_calls);

auto f = once(&HolderOfTruth::getTruth, 6);

auto g = once(&HolderOfTruth::setTruth, 3);

auto TrueHolder = new HolderOfTruth{true};

auto FakeHolder = new HolderOfTruth{false};

ASSERT_TRUE( TrueHolder->getTruth());

ASSERT_FALSE(FakeHolder->getTruth());

EXPECT_TRUE( f(TrueHolder));

EXPECT_FALSE(f(FakeHolder));

EXPECT_NO_THROW(g(TrueHolder, false));

EXPECT_NO_THROW(g(FakeHolder, true));

EXPECT_FALSE(f(TrueHolder));

EXPECT_TRUE( f(FakeHolder));

EXPECT_NO_THROW(g(TrueHolder, true));

EXPECT_NO_THROW(g(FakeHolder, false));

EXPECT_TRUE(f(TrueHolder));

EXPECT_TRUE(f(FakeHolder));

EXPECT_THROW(f(TrueHolder), out_of_calls);