I can understand this:
List("one word", "another word") unzip (_ span (_ != ' '))
But don’t get what’s happening here below in the span. span takes a predicate and I think the braces can be omitted as span is used inline and has only one parameter but why isn’t there any _ and what is ' '.!=
List("one word", "another word") unzip (_ span ' '.!=)
In Scala, operators are just special-named methods. Here ' '.!= fetches but does not apply the != to the ' ' object. This method takes one parameter and returns a boolean value.
For any function f that takes a single argument, (x => f(x)) and f are equivalent expressions – so there is no need to wrap such a function into another lambda.
The span method takes a predicate, and partitions a sequence (here: String) into a prefix that satisfies the predicate, and a suffix that doesn’t. Here we want to get the string up to the first space.
- In the first line, we use the predicate
(_ != ' '), more clearly(c => c != ' '). - We can now swap the arguments of the inequality “operator”, as this operation should be reflexive. We now have:
(c => ' ' != c). - We can now use the explicit method call syntax:
(c => ' '.!=(c)). -
Next, we save that method in another variable:
val f: (Char => Boolean) = ' '.!= ... (c => f(c)) -
As stated above,
fand(c => f(c))are equivalent, therefore(_ != ' ')and' '.!=must be equivalent too.
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