I have two kinds of definition of a three-parameter function as below:

val minus1: (Int, Int, Int) => Int = _ - _ - _
val minus2: (Int, Int, Int) => Int = （_ - _） - _

minus1 is fine, but minus2 is reported illegal, that confused me a lot

Following ComDubh's insturction, i write a new function like:

val minus3 : (Int, Int, Int)=>Int = ((_-_)-_)

why this was still wrong? Did that mean i shouldn't put any parenthese between the "_"s? and i have a more complicated question like

val func4: Int=>Int = x => if (x>0) 1 else -1
val func5: Int=>Int = if (_>0) 1 else -1

func4 is good, but why i can't omit the parametr name "x" to rewrite the function as func5(the compiler regards the 1 or -1 as the return value and reports Int(1) doesn't fit Int=>Int). Thans for your time

CodePudding user response：

You're creating an anonymous function. Scala has to know where the definition of the anonymous function starts and ends. Your use of parentheses in minus2 tells Scala that _ - _ is the complete function. The compiler isn't happy of course as you're missing an argument.