Is there a tuple unpacking for function calls?

[denfren]

Can tuples be unpacked, so that varargs can be passed on?

foo = |args...| os.command("echo").args( args ).wait_for_exit()
foo "hello", "world"

[irh]

Hi @denfren 👋

Good question, it would seem natural for .args to accept the variadic argument given that it is itself a variadic function.

The current rule for varargs is simple but limited, the varargs get rolled into a tuple, and then it's passed around as a regular non-magic value.

It would be possible to introduce an unpacking operator, reusing ...:

foo = |args...| os.command("echo").args( args... #- args are unpacked here -# ).wait_for_exit()
foo "hello", "world"

It would be a very niche feature but might be the only way to make it possible to call a variadic function from another variadic function.. In your example there's the workaround of looping over the varargs, but that only works given that command.args can be called repeatedly:

foo = |args...|
  echo = os.command("echo")
  for arg in args
    echo.args(arg)
  echo.wait_for_exit()
foo "hello", "world"

But if you could only call it once then there wouldn't be a way to pass the varargs along:

f = |args...|
  for i, arg in args.enumerate()
    print '{i}: {arg}'
    
g = |args...| 
  f args

f 'one', 'two', 'three'
g 'one', 'two', 'three'

# 0: one
# 1: two
# 2: three
# 0: ('one', 'two', 'three')

So I think this simply is a missing feature.

[irh]

I created an issue to implement this, #418.