Is there a reason for not support multi-assignment on select statement?

Help & Support
1

Following is a reduced example:

chan = Channel(Tuple(String, String)).new

a = spawn(name: "spawn1") do
  sleep rand(10)
  chan.send({"spawn1", "a"})
end

b = spawn(name: "spawn1") do
  sleep rand(10)
  chan.send({"spawn2", "b"})
end

2.times do
  select
  when a, b = chan.receive
    pp! a, b
  end
end

Get following error:

In 1.cr:15:8

 15 | when a, b = chan.receive
           ^
Error: invalid select when expression: must be an assignment or call

Thanks.