Minor improvements to All and Any adapters
#2782
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…rcuit These futures should panic if they are polled after completing. Currently they do so but only if they complete due to exhausting the `Stream` that they pull data from. If they complete due to short-circuiting, they are left in a state where `fut` and `accum` are still `Some`. This means that if they are polled again, they end up polling the inner `fut` again. That usually causes a panic but the error message will likely reference the internal `Future`, not `All` / `Any`. With this commit, `All` and `Any`'s internal state will be set such that if they are polled again after completing, they will panic without polling `fut`.
It looks like `All` was originally implemented by copying from `TryFold` from which it inherited its `accum` field. However, `accum` can only ever be one of two values: `None` (if `All` has already completed) or `Some(true)` (if it's still processing values from the inner `Stream`). It doesn't need to keep track of an accumulator because the very fact that it hasn't short-circuited yet means that the accumulated value can't be `Some(false)`. Therefore, we only need two values here and we can represent them with a `bool` indicating whether or not `All` has already completed. The same principle applies for `Any` but substituting `Some(false)` for `Some(true)`.
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I found a few things in the implementation for these adapters that I thought could be improved while adding
TryAllandTryAny.