在下面的代码片段中，我看到了这种Unit类型，但无法确定何时使用它以及它在做什么？我阅读了https://github.com/facebook/folly/blob/master/folly/Unit.h，但仍然不知道如何在程序中使用此Unit。单位可以提供哪些典型方案？
Future<Unit> fut3 = std::move(fut2)
.thenValue([](string str) {
cout << str << endl;
})
.thenTry([](folly::Try<string> strTry) {
cout << strTry.value() << endl;
})
.thenError(folly::tag_t<std::exception>{}, [](std::exception const& e) {
cerr << e.what() << endl;
});
最佳答案
这直接来自comments on the class itself，并解释了包括用例在内的几乎所有内容。
/// In functional programming, the degenerate case is often called "unit". In
/// C++, "void" is often the best analogue. However, because of the syntactic
/// special-casing required for void, it is frequently a liability for template
/// metaprogramming. So, instead of writing specializations to handle cases like
/// SomeContainer<void>, a library author may instead rule that out and simply
/// have library users use SomeContainer<Unit>. Contained values may be ignored.
/// Much easier.
///
/// "void" is the type that admits of no values at all. It is not possible to
/// construct a value of this type.
/// "unit" is the type that admits of precisely one unique value. It is
/// possible to construct a value of this type, but it is always the same value
/// every time, so it is uninteresting.
关于c++ - 何时使用愚蠢的单位类型，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/59937064/