Robert Klemme
2/22/2006 1:00:00 PM
listrecv@gmail.com wrote:
> A few simple syntax questions:
>
> 1) Anyway to do use the default arg for nonlast params? Something
> like:
> run(xyz, , 3)
No. You have to use one form of keyword arguments (for example by using a
hash). Note that proper support for this is likely to happen in Ruby 2.0.
> 2) Veru often I see things like:
> a, b = meth()
> Is meth returning two objects? Or is it returning one object - like a
> tuple or something - which the parser automagically splits into a & b?
> What are the rules of using two vars with commas together?
It's a combination of parallel assignment with multiple return values.
# parallel assignment
a,b,c=1,2,3
a,b,c=[1,2,3]
# multiple return values
def mu1
return 1,2,3
end
def mu2
[1,2,3]
end
def mu3
return [1,2,3]
end
irb(main):015:0> a,b,c = mu1
=> [1, 2, 3]
irb(main):016:0> a
=> 1
irb(main):017:0> b
=> 2
irb(main):018:0> c
=> 3
irb(main):019:0> a,b,c = mu2
=> [1, 2, 3]
irb(main):020:0> a
=> 1
irb(main):021:0> b
=> 2
irb(main):022:0> c
=> 3
irb(main):023:0> a,b,c = mu3
=> [1, 2, 3]
irb(main):024:0> a
=> 1
irb(main):025:0> b
=> 2
irb(main):026:0> c
=> 3
The star operator can be used to collect remaining args:
irb(main):029:0> a,*b = mu1
=> [1, 2, 3]
irb(main):030:0> a
=> 1
irb(main):031:0> b
=> [2, 3]
More strictly speaking, returning anything that implements #to_ary will be
treated this way:
irb(main):032:0> class Foo
irb(main):033:1> def to_ary() ["foo",2,3] end
irb(main):034:1> end
=> nil
irb(main):035:0> def foo() Foo.new end
=> nil
irb(main):036:0> a,b,c = foo
=> ["foo", 2, 3]
irb(main):037:0> a
=> "foo"
irb(main):038:0> b
=> 2
irb(main):039:0> c
=> 3
HTH
Kind regards
robert