isFirst method
Return true if the given item
is the same (by identity) as the first iterable item.
If this iterable is empty, always return null.
This is useful for non-indexed loops where you need to know when you have the first item.
For example:
for (student in students) {
if (!children.isFirst(student) result.add(Divider());
result.add(Text(student.name));
}
Implementation
bool isFirst(T item) => length > 0 && identical(first, item);