with val syntax sugar for more complex types #707
Description
Problem statement
There's no way to unpack more complex types the using with val _ = ... syntax sugar.
Motivation
When working with stream, I tried to do something like:
def main() = {
with val (i, x) = [(1, 'a'), (2, 'b'), (3, 'c')].foreach;
println(show(i) ++ ": " ++ show(x))
}in order to unpack the tuple.
However, that's wrong since this sugar would imply that foreach takes two arguments
as it desugars to something like:
...foreach { (i, x) => ... }But the correct diet, sugar-free version is the following:
def main() =
[(1, 'a'), (2, 'b'), (3, 'c')].foreach { case (i, x) =>
println(show(i) ++ ": " ++ show(x))
}Possible and impossible workarounds
I tried to remedy this by using Tuple2(i, x) explicitly, but that reports a parse error:
def main() = {
with val Tuple2(i, x) = [(1, 'a'), (2, 'b'), (3, 'c')].foreach;
// ^ Expected = but got (
println(show(i) ++ ": " ++ show(x))
}Similarly if I try to use a custom type:
record Pos(i: Int, x: Char)
def main() = {
with val Pos(i, x) = [Pos(1, 'a'), Pos(2, 'b'), Pos(3, 'c')].foreach;
// ^ Expected = but got (
println(show(i) ++ ": " ++ show(x))
}What does work is the following:
def main() = {
with val tup = [(1, 'a'), (2, 'b'), (3, 'c')].foreach;
val (i, x) = tup;
println(show(i) ++ ": " ++ show(x))
}