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→C++: Add updates to C++20/C++23 support for coroutines and generators. |
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===C===
[[C (programming language)|C]] does not have generator functions as a [[language construct]], but, as they are a subset of [[coroutines]], it is simple to implement them using any framework that implements stackful coroutines, such as libdill.<ref>{{cite web|url=http://libdill.org|title=Structured Concurrency for C}}</ref> On POSIX platforms, when the cost of [[context switching]] per iteration is not a concern, or full [[Parallel_computing|parallelism]] rather than merely [[Concurrency (computer_science)|concurrency]] is desired, a very simple generator function framework can be implemented using [[pthreads]] and [[Anonymous_pipe|pipes]].
===C++===
It is possible to introduce generators into C++ using pre-processor macros. The resulting code might have aspects that are very different from native C++, but the generator syntax can be very uncluttered.<ref>{{Cite web|url = http://www.codeproject.com/KB/cpp/cpp_generators.aspx|title = Generators in C++|date = 21 September 2008|access-date = 9 January 2012|archive-date = 7 February 2019|archive-url = https://web.archive.org/web/20190207185018/https://www.codeproject.com/KB/cpp/cpp_generators.aspx|url-status = dead}}</ref> The set of pre-processor macros defined in this source allow generators defined with the syntax as in the following example:
<syntaxhighlight lang="cpp">$generator(descent) {
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int operator*() const { return iter; }
};
</syntaxhighlight>Furthermore, [[C++20]] formally introduced support for coroutines,<ref>{{Cite web |title=Coroutines (C++20) - cppreference.com |url=https://en.cppreference.com/w/cpp/language/coroutines.html |access-date=2025-07-16 |website=en.cppreference.com}}</ref>
#include <generator>
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| otherwise = []
</syntaxhighlight>
which walks down the list and stops on the first element that doesn't satisfy the predicate. If the list has been walked before until that point, it is just a strict [[data structure]], but if any part hadn't been walked through before, it will be generated on demand. List comprehensions can be freely used:
<syntaxhighlight lang="haskell">
squaresUnder20 = takeWhile (<= 20) [x * x | x <- countFrom 10]
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===F#===
{{further information|Sequence expression}}
[[F Sharp (programming language)|F#]] provides generators via ''[[sequence expression]]s,'' since version 1.9.1.<ref name="seq">{{cite web | url = http://blogs.msdn.com/dsyme/archive/2007/09/22/some-details-on-f-computation-expressions-aka-monadic-or-workflow-syntax.aspx | title = Some Details on F# Computation Expressions | access-date = 2007-12-14}}</ref> These can define a sequence (lazily evaluated, [[sequential access]]) via <code>seq { ... }</code>, a list (eagerly evaluated, sequential access) via <code>[ ... ]</code> or an array (eagerly evaluated, indexed access) via <code>[| ... |]</code> that contain code that generates values. For example,
<syntaxhighlight lang="fsharp">
seq { for b in 0 .. 25 do
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