Invalidating iterators c
Various types of iterators are often provided via a container's interface.Though the interface and semantics of a given iterator are fixed, iterators are often implemented in terms of the structures underlying a container implementation and are often tightly coupled to the container to enable the operational semantics of the iterator.An iterator performs traversal and also gives access to data elements in a container, but does not itself perform iteration (i.e., not without some significant liberty taken with that concept or with trivial use of the terminology) Internal iterators are higher order functions (often taking anonymous functions) such as map, reduce etc., implementing the traversal across a container, applying the given function to every element in turn.An external iterator may be thought of as a type of pointer that has two primary operations: referencing one particular element in the object collection (called element access), and modifying itself so it points to the next element (called element traversal).is, at least not necessarily (and I’m currently unsure whether it’ a legal implementation).In libstdc , at least, a deque is implemented as a vector of vectors, i.e. It should be noted that this fixed block size depends on the size of the element type, and is very small for even moderately large types (it’s Just because they say std::vector is a good default, doesn't make it perfect for everything.
By using an iterator one is isolated from these sorts of consequences.
std::deque can be manipulated at the front and even does so without invalidating iterators c.
std::deque doesn't grow exponentially thus wasting less space and being less susceptible to a fragmented heap. std::deque may return memory when shrinking I'm sure there's more if I dug a bit. N3936 22.214.171.124 [deque.modifiers]/1: "An insertion at either end of the deque invalidates all the iterators to the deque, but has no effect on the validity of references to elements of the deque."I have to grumble at this, because "exponentially" usually means "bad", but in vector's context it's good.
In Python, an iterable is an object which can be converted to an iterator, which is then iterated through during the for loop; this is done implicitly.
Or other times they may be created by the collection object itself, as in this Ruby example: This iteration style is sometimes called "internal iteration" because its code fully executes within the context of the iterable object (that controls all aspects of iteration), and the programmer only provides the operation to execute at each step (using an anonymous function).
This effectively reduces the container size by the number of elements removed, which are destroyed.