Generator (computer programming): Difference between revisions

Revision as of 08:36, 23 January 2021

Revision as of 17:47, 11 June 2021

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===Java===

Java has had a standard interface for implementing iterators since its early days, and since Java 5, the "foreach" construction makes it easy to loop over objects that provide the <ttcode>java.lang.Iterable</ttcode> interface. (The [[Java collections framework]] and other collections frameworks, typically provide iterators for all collections.)

However, [[Java (programming language)|Java]] does not have generators built into the language. This means that creating iterators is often much trickier than in languages with built-in generators, especially when the generation logic is complex. Because all state must be saved and restored every time an item is to be yielded from an iterator, it is not possible to store state in local variables or use built-in looping routines, as when generators are available; instead, all of this must be manually simulated, using object fields to hold local state and loop counters.

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In Python, a generator can be thought of as an [[iterator]] that contains a frozen [[stack frame]]. Whenever <code>next()</code> is called on the iterator, Python resumes the frozen frame, which executes normally until the next <code>yield</code> statement is reached. The generator's frame is then frozen again, and the yielded value is returned to the caller.

PEP 380 (implemented in Python 3.3) adds the <ttcode>yield from</ttcode> expression, allowing a generator to delegate part of its operations to another generator or iterable.<ref name="pep380">[https://www.python.org/dev/peps/pep-0380/ PEP 380 -- Syntax for Delegating to a Subgenerator]</ref>

====Generator expressions====