I have a function that should return all but the first argument
foo = -> arguments[1..]
foo(0,1,2,3,4)
unfortunately arguments is not an array but an object.
What is the best way to convert the object into an array?
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3 Answers
There are a few CoffeeScript-ish options using a splat to take care of array-ifying arguments. You can use slice:
f = (args...) -> args.slice(1)
Or you could use a range instead of directly calling slice:
f = (args...) -> args[1..-1]
You can simplify the second version because:
Slices indices have useful defaults. An omitted first index defaults to zero and an omitted second index defaults to the size of the array.
So you could leave off the -1 and say just:
f = (args...) -> args[1..]
instead. Thanks to scar3tt for pointing this out.
4 Comments
mu is too short
@Wex: True but I think there's something to be said for the "I'm a variadic function" explicitness of
(args...) that directly using arguments doesn't always give you.
Michael_Scharf
interesting, the
args... is essentially turned into [].slice.call(arguments) by the coffeescript compiler
mu is too short
@scarl3tt: I think I missed that. The only relevant thing I can find in the ChangeLog is "Both endpoints of a slice are now allowed to be omitted for consistency, effectively creating a shallow copy of the list." and that was from 1.3.1 on April 10, 2012 (i.e. about a year before this answer). Let me patch things up a bit.
You can ignore the first argument and use splats to capture the rest:
foo = (_, rest...) -> rest
You could also do something like foo = (args...) -> args[1...], but that'll compile to two different calls to Array#slice (unlike the first snippet).
2 Comments
Michael_Scharf
that is a great answer if I only want to ignore the rest of the arguments. I used the
[1...] just to illustrate that I cannot do array operations...
epidemian
@Michael_Scharf, ha, OK. Then yeah, the idiomatic way to treat
arguments as an array in CoffeeScript is to simply declare the function as (args...) -> and then use args which is a real array.What found is to use Array.prototype.slice:
coffee> foo = -> Array.prototype.slice.apply(arguments)[1..]
[Function]
coffee> foo(0,1,2,3,4)
[ 1, 2, 3, 4 ]
Another version would be
[].slice.call(arguments)
1 Comment
mu is too short