Rewrote higher-order-functions #699
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removed illegal characters
…a.github.com into higher-order-functions
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| Higher order functions take other functions as parameters or return a function as | ||
| a result. This is possible because functions are first-class values in Scala. | ||
| One of the most common examples is the higher-order |
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examples (without “s”).
Or, I would just say “A common example …”
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Hmm.. maybe I'm missing something but just so it's clear One of the most common examples with the s is the correct English.
That said, you can certainly say A common example...
| Since the Scala compiler already knows the type of the parameters (a single Int), | ||
| you just need to provide the right side of the function. The only | ||
| caveat is that you need to use `_` in place of a parameter name (it was `x` in | ||
| the previous example). |
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Why is this a “caveat”?
Maybe a more intuitive way to describe the _ * 2 syntax is to say that _ means “a hole”, thus the expression _ * 2 means “something (that has to be filled in), multiplied by two”
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I've heard the hole metaphor used before and I don't think it's used outside of Scala documentation.
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But yes, it should be reworded.
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Just use "difference" instead of "caveat".
If you want to make it more clear, you could also add Julien's explanation but call it a "slot" that has to be filled.
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| The new function, `promotion`, takes the salaries plus a function of type `Double => Double` | ||
| (i.e. a function that takes a Double and returns a Double) and returns the product. |
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What do you mean by “returns the product”?
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it returns the product of the current salary multiplied by a factor. I guess it could be clearer to say it returns the new salary.
| ```tut | ||
| object SalaryRaiser { | ||
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| private def promotion(salaries: List[Double], promotionFunction: Double => Double): List[Double] = |
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This is a poor example because the resulting code is more verbose and harder to follow. Abstraction in examples should lead to a very clear win to help motivate the feature.
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@Ichoran I agree with that point. Can you think of a better example?
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Maybe do something with case class Point(x: Double, y: Double) and def closestBy(points: List[Point], target: Point, metric: (Point, Point) => Double? Then you can have closestByDistance(points: List[Point], target: Point) = closestBy(points, target, (p, q) => (p.x - q.x)*(p.x - q.x) + (p.y - q.y)*(p.y - q.y) and for closestByBlock math.abs(p.x - q.x) + math.abs(p.y-q.y) and so on.
Whatever you choose, the key should be that the work of the common function shouldn't be completely trivial (i.e. it should be more than just one other method call!).
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@Ichoran Yeah, nice example! @travis032654 Maybe we can also mention that this is an application of the Strategy design pattern, do you think that would help enterprise programmers to get it?
| of a method that returns a function. | ||
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| ```tut | ||
| def urlBuilder(ssl: Boolean, domainName: String): (String, String) => String = { |
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This is not a good example because you would almost never see this. Instead, you'd just write urlBuilder(ssl: Boolean, domainName: String): String and get the function above with urlBuilder _.
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There was some good feedback on this that never got addressed, but it's still an improvement, as-is, so I figure hitting "merge" is better than just letting it languish forever. I invite anyone watching the repo to submit a followup PR with further improvements, whether suggested by reviewers here or otherwise. |
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