If you want an Iterator over an array, you could use one of the direct implementations out there instead of wrapping the array in a List. For example: Apache Commons Collections ArrayIterator Or, this one, if you’d like to use generics: com.Ostermiller.util.ArrayIterator Note that if you want to have an Iterator over primitive types, you … Read more
By convention a “NULL iterator” for containers, which is used to indicate no result, compares equal to the result of container.end(). std::vector<X>::iterator iter = std::find(my_vec.begin(), my_vec.end(), x); if (iter == my_vec.end()) { //no result found; iter points to “nothing” } However, since a default-constructed container iterator is not associated with any particular container, there is … Read more
Following is the quote from Nicolai Josuttis book: Note that advance() does not check whether it crosses the end() of a sequence (it can’t check because iterators in general do not know the containers on which they operate). Thus, calling this function might result in undefined behavior because calling operator ++ for the end of … Read more
You have two options, using the Object.keys() and then forEach, or use for/in: class stationGuide { station1: any; station2: any; station3: any; constructor(){ this.station1 = null; this.station2 = null; this.station3 = null; } } let a = new stationGuide(); Object.keys(a).forEach(key => console.log(key)); for (let key in a) { console.log(key); } (code in playground)
Iteration’s support for __getitem__ can be seen as a “legacy feature” which allowed smoother transition when PEP234 introduced iterability as a primary concept. It only applies to classes without __iter__ whose __getitem__ accepts integers 0, 1, &c, and raises IndexError once the index gets too high (if ever), typically “sequence” classes coded before __iter__ appeared … Read more
The discussed alternatives are clear but I feel that a code example is needed. Given that there will not be a language substitute and without relying on boost or on your own version of iterator base class, the following code that uses std::iterator will be fixed to the code underneath. With std::iterator template<long FROM, long … Read more
Iterating means repeating some steps, while enumerating means going through all values in a collection of values. So enumerating usually requires some form of iteration. In that way, enumerating is a special case of iterating where the step is getting a value from a collection. Note the “usually” – enumerating may also be performed recursively, … Read more
Short of iterating through the iterable and counting the number of iterations, no. That’s what makes it an iterable and not a list. This isn’t really even a python-specific problem. Look at the classic linked-list data structure. Finding the length is an O(n) operation that involves iterating the whole list to find the number of … Read more
So I have a somewhat reasonable explanation now: Short version: Because the syntax also applies to arrays, which don’t have iterators. If the syntax were designed around Iterator as I proposed, it would be inconsistent with arrays. Let me give three variants: A) as chosen by the Java developers: Object[] array; for(Object o : array) … Read more
begin will return an iterator or a const_iterator depending on the const-qualification of the object it is called on. cbegin will return a const_iterator unconditionally. std::vector<int> vec; const std::vector<int> const_vec; vec.begin(); //iterator vec.cbegin(); //const_iterator const_vec.begin(); //const_iterator const_vec.cbegin(); //const_iterator