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#Polymorphism array
shy joltBOT
pliant jackal
You can't. Arrays are of a fixed type, can't have an array with different types. There are various workarounds. One way is to make 2 arrays, one for Children and one for Parents and then iterating over both. Another way is to make an std::array<std::unique_ptr<Child>>.
vapid kelp
I'm not trying to make an array that has more than one type
I'm trying to make an init function that would work for either
pliant jackal
Make 2 functions and rely on overloading. For the user it will look like init can take both Parent and Child pointers.
There are also ways to de-duplicate the code should that be necessary.
vapid kelp
like what
pliant jackal
Like factoring the inside, arr[i].a = 0; in this case, into a separate function, say void handle(Child *c);
Doesn't seem worth it in the example case because the inside is so small.
Another way is to make init a template and restrict its input to Child * and Parent *.
vapid kelp
I thought about using templates, is there a downside to that?
pliant jackal
It's more messy than using an overloaded function for this case.
You don't actually need the flexibility because the set of types is known.
And users can be dumb and explicitly use init<Child*>(parents, std::size(parents));
vapid kelp
okay
pliant jackal
The standard library would use a pair of iterators here.
I find that ugly, but it's flexible and works.
vapid kelp
what do you mean?
pliant jackal
template <class Iterator>
void init(Iterator begin, Iterator end) {
while (begin != end) {
begin->a = 0;
}
}
init(std::begin(arr), std::end(arr));
This works for both Parent[] and Child[].
rich hatch
Semi off topic but another way is to make a constructor
If there aren't many ways to "init", that actually works rather well
If for whatever reason you need the two step
- default construction, then
- explicit init call
I would probably recommend making a template to iterate through the array and call the init function
Technically there's a way to accept only builtin arrays, if you're dealing with those only, but if you start having dynamically allocated objects/arrays, that can be inconvenient in multiple ways
rich hatch
Semi off topic but another way is to make a constructor
Probably the main reason why the constructor is preferred, is to make it impossible to forget to call "init"
shy joltBOT
@vapid kelp
vapid kelp
!solved