On Friday, 22 November 2024 at 16:36:43 UTC, Andrew wrote:
I'm getting started using D for some small personal projects
and one thing I wanted to do was use a helper function for a
tuple. I declared the function like this:
string getOrZeroth(Tuple!(string, string, string) tup, int
i) pure {
return tup[i] == "" ? tup[0] : tup[i];
}
and would like to use it like this:
auto foo = tuple("a", "", "c");
writeln(foo.getOrZeroth(1)); // prints a
but when I try it, I'm getting the below error:
Error: variable \`i\` cannot be read at compile time
It would probably make more sense to create a class and make
that a member function, but at this point I'm mostly just
curious about how to use a tuple as a function parameter. I
tried using a couple different options like `tuple` and
`TypeTuple` as well as trying to convert the function into a
template, but didn't have any better luck with those. I feel
like I'm probably missing something silly, and any help would
be appreciated.
tuples elements must be retrieved with indexes that are known at
compile time (integer literals or enum members). You pass one but
this becomes a value that's not known inside the body
so you can use a template value parameter instead:
```
string getOrZeroth(int i)(Tuple!(string, string, string) tup)
{
return tup[i] == "" ? tup[0] : tup[i];
}
```
and use it like that:
```
writeln(foo.getOrZeroth!(1)); // prints a
```
