Update fp-pure-functions.md #2009
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The discussion of impurity was technically not correct. `foreach` alone is not impure. Also `const Unit` is a perfectly pure function. So we need to be a bit more precise here in order to not confuse beginners.
julienrf
approved these changes
May 10, 2021
| @@ -50,24 +50,20 @@ Most methods on the Scala collections classes also work as pure functions, inclu | |||
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| Conversely, the following functions are _impure_ because they violate the definition. | |||
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| The `foreach` method on collections classes is impure because it’s only used for its side effects, such as printing to STDOUT. | |||
| - `println` -- methods that interact with the console, files, databases, web services, sensors, etc., are all impure. | |||
| - `getHour` -- date and time related methods are all impure because their output depends on something other than their input parameters | |||
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Calling getHour on a LocalTime always returns the same value, so this might be confusing. Consider maybe using currentTimeMillis?
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Thanks you are, I was just using those since @alvinj mentioned them in the original doc.
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Thanks, currentTimeMillis is a much more obvious example!
b-studios
commented
May 10, 2021
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The discussion of impurity was technically not correct.
foreachalone is not impure.Also
const Unitis a perfectly pure function.So we need to be a bit more precise here in order to not confuse beginners.