Simplify reduce and add min_by and max_by #306
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Since `sum` and `product` became their own things, `reduce` doesn't need the `ReduceOp` abstraction any more.
We can use a simpler match with `fold` in implementing `reduce_with`, before passing to the more complicated match where both sides are options. This may help the compiler optimize better.
These call a user's function to compare values, just like the methods added to `Iterator` in Rust 1.15.0.
| (Some(v), None) | (None, Some(v)) => Some(v), | ||
| (None, None) => None, | ||
| }) | ||
| self.fold(|| None, |opt_a, b| match opt_a { |
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It seems like a waste to wrap values in Some only to immediately match that away. It requires inlining and optimization to realize that the right side always has something while folding. In practice, I couldn't measure a difference, so I'll drop this change if you prefer.
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I see. That's true. I don't have a strong opinion, just curious. I agree that it seems like this formulation might unlock some optimization somehow.
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