> There are plenty of cases in real-world code where an array that's part of a struct or object may or may not contain any elements. If you're just parsing input into that, it seems like you'd either still end up doing an equivalent of checking whether the array is empty or not everywhere the array might be used later, even if that check is looking at an "array has elements" type flag in the struct/object, and so you're still maintaining a description of ways that the input may be invalid.
You only check it if it makes a difference to validity or not. There's no scenario where you keep the array and a parallel flag - either an empty array is invalid in which case you refuse to construct if it's empty, or an empty array is valid in which case you don't even check. Same thing for if you're checking whether it's got an even number of elements, got less than five elements, etc. - you don't keep the flag around, you refuse to construct your validated structure (even if that "validated structure" is actually just a marker wrapper around the raw array, if your type system isn't good enough to express the real constraint directly).
You only check it if it makes a difference to validity or not. There's no scenario where you keep the array and a parallel flag - either an empty array is invalid in which case you refuse to construct if it's empty, or an empty array is valid in which case you don't even check. Same thing for if you're checking whether it's got an even number of elements, got less than five elements, etc. - you don't keep the flag around, you refuse to construct your validated structure (even if that "validated structure" is actually just a marker wrapper around the raw array, if your type system isn't good enough to express the real constraint directly).