Dotty (Scala 3) v20 for/do loop syntax

By Alvin Alexander. Last updated: November 26, 2019

Just fooling around a little bit at the moment, here are several ways to write for/do blocks with the “significant indentation” style in Dotty (Scala 3) as of Dotty v20:

import io.Source

def printLines1(source: Source): Unit =
    for line <- source.getLines do println(line)

def printLines2(source: Source): Unit =
    for line <- source.getLines
    do println(line)
    
def printLines3(source: Source): Unit =
    for line <- source.getLines
    do
        println(line)
        
def printLines4(source: Source): Unit =
    for
        line <- source.getLines
    do
        println(line)
        
def printLines5(source: Source): Unit =
    for
        line <- source.getLines
        if line.trim != ""
    do
        // a multiline `do` block
        println("in `do` block of `for`")
        println(line)

There’s nothing earth-shattering there. I started down this road because I didn’t know what the syntax was for a one-line for/do loop, and after that I became interested in the syntax for the other examples, including the last multiline for/do loop.

scala

for

for loop

syntax

dotty

scala 3

significant indentation

Dotty (Scala 3) v20 for/do loop syntax

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