Enumerator generator

I'm using [fff](https://github.com/meekrosoft/fff) to mock a call and I have a `std::vector` of expected arguments for the mocked function. The way fff works, I need a generator that works like the Python `enumerate` statement: on each iteration it returns the iteration number and an element of my vector, so my test goes something like this:

```c++
REQUIRE(my_function_fake.arg0_history[i] == val_a);
REQUIRE(my_function_fake.arg1_history[i] == val_b);
```

I need both the vector element and the index. I'm trying to understand how to best go about it. My first try was to simply iterate over the vector and use `CAPTURE`:

```c++
uint32_t factorial(uint32_t number)
{
return number <= 1 ? number : factorial(number - 1) * number;
}

TEST_CASE("Factorials are computed", "[factorial]")
{
std::vector> expected_results = {
{1, 1},
{2, 2},
{3, 6},
{10, 3'628'800+1}, // Bad value
};

for( int i = -1; const auto& v : expected_results ) {
++i;
auto& [input, expected] = v;
CAPTURE(i, input, expected);
REQUIRE(factorial(input) == expected);
}
```

This works great, I get a nice error message with the particular values that failed:

```
test.cc:50: FAILED:
REQUIRE( factorial(input) == expected )
with expansion:
3628800 (0x375f00) == 3628801 (0x375f01)
with messages:
i := 3
input := 10
expected := 3628801 (0x375f01)
```

Using the `range` generator seems a bit overly complicated:

```c++
size_t i = GENERATE_REF(Catch::Generators::range(static_cast(0), expected_results.size()));
auto [input, expected] = expected_results[i];
CAPTURE(i, input, expected);
REQUIRE(factorial(input) == expected);
```

Is there a way to use one of the `GENERATE` macros for this?

Thanks!