Hi everybody.
What means this snippet of code? Why use the "star" ?
myarray = [1,2,3,4,5,6,6]
qa = *myarray
Thank you.
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"“Machines take me by surprise with great frequency.” A. Turing
Mirko Viviani wrote:
Hi everybody.
What means this snippet of code? Why use the "star" ?myarray = [1,2,3,4,5,6,6]
qa = *myarrayThank you.
In this example it doesn't really do anything, i think. Normally you
would use the * in an argument list, in a method definition, to
effectively say 'pull all arguments after this into a single array', eg
def foo(mainarg, *otherargs)
puts mainarg.inspect
puts otherargs.inspect
end
=> nil
foo(1,2,3,4,5,6)
1
[2, 3, 4, 5, 6]
=> nil
In this sense it's like * in a regular expression, meaning 'any number
of arguments'. That's how i understand it anyway, a more precise
description will probably be forthcoming 
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Hi --
Hi everybody.
What means this snippet of code? Why use the "star" ?myarray = [1,2,3,4,5,6,6]
qa = *myarray
In addition to the examples in the other answers, note that the star
has some new behavior in 1.9.
Here's the 1.8 behavior.
*a = 1; a
=> [1]
*a = [1]; a
=> [[1]]
*a = [[1]]; a
=> [[[1]]]
In each case, the star indicates one "missing" level of array
wrapping. In 1.9, that's changed:
*a = 1; a
=> [1]
*a = [1]; a
=> [1]
*a = [[1]]; a
=> [[1]]
*a = 1 and *a = [1] have the same result. (I know there was a lot of
discussion about this when it was being changed but I can't remember
exactly what the rationale was.)
David
On Thu, 23 Jul 2009, Mirko Viviani wrote:
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Sorry,
Complete code was like this
x, *xs = *myarray
after executing, x is 1 and xs [2,3,4,5,6,6] ..... :o
2009/7/23 Max Williams <toastkid.williams@gmail.com>
Mirko Viviani wrote:
> Hi everybody.
> What means this snippet of code? Why use the "star" ?
>
> myarray = [1,2,3,4,5,6,6]
> qa = *myarray
>
> Thank you.In this example it doesn't really do anything, i think. Normally you
would use the * in an argument list, in a method definition, to
effectively say 'pull all arguments after this into a single array', eg>> def foo(mainarg, *otherargs)
>> puts mainarg.inspect
>> puts otherargs.inspect
>> end
=> nil
>> foo(1,2,3,4,5,6)
1
[2, 3, 4, 5, 6]
=> nilIn this sense it's like * in a regular expression, meaning 'any number
of arguments'. That's how i understand it anyway, a more precise
description will probably be forthcoming
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--
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***********************************************
"“Machines take me by surprise with great frequency.” A. Turing
Mirko Viviani schrieb:
Sorry,
Complete code was like this
x, *xs = *myarrayafter executing, x is 1 and xs [2,3,4,5,6,6] ..... :o
Mirko Viviani wrote:
Hi everybody.
What means this snippet of code? Why use the "star" ?myarray = [1,2,3,4,5,6,6]
qa = *myarrayThank you.
In this example it doesn't really do anything, i think. Normally you
would use the * in an argument list, in a method definition, to
effectively say 'pull all arguments after this into a single array', egdef foo(mainarg, *otherargs)
puts mainarg.inspect
puts otherargs.inspect
end
=> nil
foo(1,2,3,4,5,6)
1
[2, 3, 4, 5, 6]
=> nilIn this sense it's like * in a regular expression, meaning 'any number
of arguments'. That's how i understand it anyway, a more precise
description will probably be forthcoming
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irb(main):001:0> x = 0
=> 0
irb(main):002:0> xs = [0, 0]
=> [0, 0]
irb(main):003:0> myarray = [1, 2, 3]
=> [1, 2, 3]
irb(main):004:0> x, *xs = *myarray
=> [1, 2, 3]
irb(main):005:0> x
=> 1
irb(main):006:0> xs
=> [2, 3]
irb(main):007:0> x = 0
=> 0
irb(main):008:0> xs = [0, 0]
=> [0, 0]
irb(main):009:0> x, xs = myarray => [1, 2, 3]
irb(main):010:0> x
=> 1
irb(main):011:0> xs
=> 2
The * is also called the "splat operator". It is used to split up an array in is parts or
the other way round (like in the method definition already posted). You could also
do things like:
def foo(x, y)
puts x
puts y
end
ary = [1, 2]
foo(ary) #=> ArgumentError
foo(*ary) #=> 1, 2
Marvin
2009/7/23 Max Williams <toastkid.williams@gmail.com>
Mirko Viviani wrote:
Sorry,
Complete code was like this
x, *xs = *myarrayafter executing, x is 1 and xs [2,3,4,5,6,6] ..... :o
Ah, well there you go. In ruby, you can assign multiple variables to
multiple values simultaneously: effectively on the left side of the =
you have a list of variables and on the right you have a list of values.
If the sizes of the lists don't match up then any extra values are
thrown away and any extra variables are set to nil. eg
However, if you use the * on the rightmost variable, then any extra
values get pulled into an array and that variable points to that array:
a, b, c = 1, 2, 3
=> [1, 2, 3]
puts a.inspect; puts b.inspect; puts c.inspect
1
2
3
=> nil
a, b, c = 1, 2
=> [1, 2]
puts a.inspect; puts b.inspect; puts c.inspect
1
2
nil
=> nil
a, b = 1, 2, 3
=> [1, 2, 3]
puts a.inspect; puts b.inspect
1
2
=> nil
a, *b = 1, 2, 3
=> [1, 2, 3]
puts a.inspect; puts b.inspect
1
[2, 3]
Mirko Viviani wrote:
Sorry,
Complete code was like this
x, *xs = *myarrayafter executing, x is 1 and xs [2,3,4,5,6,6] ..... :o
x, y, z = 1, 2, 3
puts x, y, z
--output:--
1
2
3
x, y, z = *[1, 2, 3]
puts x, y, z
--output:--
1
2
3
*y = 1, 2, 3
p y
--output:--
[1, 2, 3]
x, *y = *[1, 2, 3]
puts x
p y
--output:--
1
[2, 3]
Depending on the context the * means:
a) replace an array with its individual elements
b) gather individual elements into an array
thank's to all.... this is a think I would remember 
2009/7/23 7stud -- <bbxx789_05ss@yahoo.com>
Mirko Viviani wrote:
> Sorry,
> Complete code was like this
> x, *xs = *myarray
>
> after executing, x is 1 and xs [2,3,4,5,6,6] ..... :o
>
> 2009/7/23 Max Williams <toastkid.williams@gmail.com>x, y, z = 1, 2, 3
puts x, y, z--output:--
1
2
3x, y, z = *[1, 2, 3]
puts x, y, z--output:--
1
2
3*y = 1, 2, 3
p y--output:--
[1, 2, 3]x, *y = *[1, 2, 3]
puts x
p y--output:--
1
[2, 3]Depending on the context the * means:
a) replace an array with its individual elements
b) gather individual elements into an array
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"“Machines take me by surprise with great frequency.” A. Turing
7stud -- wrote:
Depending on the context the * means:
a) replace an array with its individual elements
b) gather individual elements into an array
I said a more precise explanation would be forthcoming
7stud - am i right in thinking that if i do this
a, b = 1, 2
ruby is automatically starring just the right side of the expression,
under the hood? eg
a,b = 1,2
=> [1, 2]
puts a.inspect;puts b.inspect
1
2
=> nil
a,b = [1,2]
=> [1, 2]
puts a.inspect;puts b.inspect
1
2
=> nil
[a,b] = [1,2]
SyntaxError: compile error
(irb):37: syntax error, unexpected '=', expecting $end
[a,b] = [1,2]
^
from (irb):37
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Hi --
Depending on the context the * means:
a) replace an array with its individual elements
b) gather individual elements into an array
It's changed in 1.9. * on the left no longer has the same "un-array"
semantics.
a = [1]; a
=> [1]
*a = [1]; a
=> [1]
I'm kind of drawing a blank on why this change was made.
David
On Thu, 23 Jul 2009, 7stud -- wrote:
--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Now available: The Well-Grounded Rubyist (http://manning.com/black2\)
Training! Intro to Ruby, with Black & Kastner, September 14-17
(More info: http://rubyurl.com/vmzN\)
Max Williams wrote:
7stud - am i right in thinking that if i do this
a, b = 1, 2
ruby is automatically starring just the right side of the expression,
under the hood? eg
In pickaxe2, p. 91, the rule is:
----
When an assignment has more than one lvalue, the assignment expression
returns an array of the rvalues. Testing that out:
----
result = (x, y = [1], [2, 3])
p result
So I guess you could say "ruby is automatically starring the right hand
side of a parallel assignment if there is more than one lvalue, and the
resulting array is the value of the entire expression.
And I guess this wasn't a very good example:
x, y, z = *[1, 2, 3]
puts x, y, z
--output:--
1
2
3
Because you can eliminate the star and get the same output:
x, y, z = [1, 2, 3]
p x
p y
p z
--output:--
1
2
3
But this is where the star makes a difference:
x, y, z = 1, [2, 3]
p x
p y
p z
--output:--
1
[2, 3]
nil
x, y, z = 1, *[2, 3]
p x
p y
p z
--output:--
1
2
3
(This applies to ruby 1.8. See David Black's post for 1.9 behavior.)
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ah, cool, thanks.
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