Hi All,
Question re Array method += and
a =
=>
a += [1, 2, 3, 4]
=> [1, 2, 3, 4]
And
(a ||= ) << [1, 2, 3, 4]
=> [[1, 2, 3, 4]]
But
( a ||= ) += [ 1, 2, 3, 4 ]
SyntaxError: compile error
(irb):28: syntax error, unexpected tOP_ASGN, expecting $end
( a ||= ) += [ 1, 2, 3, 4 ]
^
from (irb):28
Why?
I guess it's a precedence issue. '<<' is a method in the Array class.
'+=' is not.
Is there alternate syntax I should use?
Thanks
SM
Simon Mullis wrote:
(a ||= ) << [1, 2, 3, 4]
=> [[1, 2, 3, 4]]
But
( a ||= ) += [ 1, 2, 3, 4 ]
SyntaxError: compile error
(irb):28: syntax error, unexpected tOP_ASGN, expecting $end
( a ||= ) += [ 1, 2, 3, 4 ]
^
from (irb):28Why?
I guess it's a precedence issue. '<<' is a method in the Array class.
'+=' is not.
The difference is that << is a method, += is an assignment. (a ||= )
returns an object, on which you can call a method, but you can't assign
to. You can only assign to the a variable itself, which (a ||= ) is
not. I guess.
mortee
Simon Mullis wrote:
Is there alternate syntax I should use?
Did you you mean this?
(a ||= ).concat [ 1, 2, 3, 4 ]
concat modifies a, like << would. It's usually faster to concatenate
than to add and reassign.
--
Florian Frank
Simon Mullis wrote:
>>> (a ||= ) << [1, 2, 3, 4]
> => [[1, 2, 3, 4]]
>
> But
>
>>> ( a ||= ) += [ 1, 2, 3, 4 ]
> SyntaxError: compile error
> (irb):28: syntax error, unexpected tOP_ASGN, expecting $end
> ( a ||= ) += [ 1, 2, 3, 4 ]
> ^
> from (irb):28
>
> Why?
>
> I guess it's a precedence issue. '<<' is a method in the Array class.
> '+=' is not.
No, it's not a precedence issue. Btw, you are comparing apples and
oranges here: += and << are not equivalent (see also further below):
irb(main):001:0> a=%w{foo bar}
=> ["foo", "bar"]
irb(main):002:0> b=a.dup
=> ["foo", "bar"]
irb(main):003:0> c=a.dup
=> ["foo", "bar"]
irb(main):004:0> b << a
=> ["foo", "bar", ["foo", "bar"]]
irb(main):005:0> c += a
=> ["foo", "bar", "foo", "bar"]
<< adds the whole Array as one object while += "appends" the Array.
You rather want Array#concat.
The difference is that << is a method, += is an assignment. (a ||= )
returns an object, on which you can call a method, but you can't assign
to. You can only assign to the a variable itself, which (a ||= ) is
not. I guess.
Exactly: the expression (a||=) is not an lvalue, i.e. cannot
assigned to. But you can do
( a ||= ).concat [ 1, 2, 3, 4 ]
Simon, please also keep in mind that += and << have different
semantics. += will create a new Array while << appends to the current
one.
Kind regards
robert
2007/10/12, mortee <mortee.lists@kavemalna.hu>:
I love this list... I send a mail, go off to a meeting, come back and
I have explanation, discussion and solution!
Thanks to all who responded.
Cheers
SM
On 10/12/07, Robert Klemme <shortcutter@googlemail.com> wrote:
2007/10/12, mortee <mortee.lists@kavemalna.hu>:
> Simon Mullis wrote:
> >>> (a ||= ) << [1, 2, 3, 4]
> > => [[1, 2, 3, 4]]
> >
> > But
> >
> >>> ( a ||= ) += [ 1, 2, 3, 4 ]
> > SyntaxError: compile error
> > (irb):28: syntax error, unexpected tOP_ASGN, expecting $end
> > ( a ||= ) += [ 1, 2, 3, 4 ]
> > ^
> > from (irb):28
> >
> > Why?
> >
> > I guess it's a precedence issue. '<<' is a method in the Array class.
> > '+=' is not.No, it's not a precedence issue. Btw, you are comparing apples and
oranges here: += and << are not equivalent (see also further below):irb(main):001:0> a=%w{foo bar}
=> ["foo", "bar"]
irb(main):002:0> b=a.dup
=> ["foo", "bar"]
irb(main):003:0> c=a.dup
=> ["foo", "bar"]
irb(main):004:0> b << a
=> ["foo", "bar", ["foo", "bar"]]
irb(main):005:0> c += a
=> ["foo", "bar", "foo", "bar"]<< adds the whole Array as one object while += "appends" the Array.
You rather want Array#concat.> The difference is that << is a method, += is an assignment. (a ||= )
> returns an object, on which you can call a method, but you can't assign
> to. You can only assign to the a variable itself, which (a ||= ) is
> not. I guess.Exactly: the expression (a||=) is not an lvalue, i.e. cannot
assigned to. But you can do( a ||= ).concat [ 1, 2, 3, 4 ]
Simon, please also keep in mind that += and << have different
semantics. += will create a new Array while << appends to the current
one.Kind regards
robert
Thanks for this Robert.
The difference between the two is exactly why I wanted to use += and
not <<. I want to add many arrays to one big one and not have to use
the extra step of Array#flatten at the end.
SM
On 10/12/07, Robert Klemme <shortcutter@googlemail.com> wrote:
2007/10/12, mortee <mortee.lists@kavemalna.hu>:
> Simon Mullis wrote:
> >>> (a ||= ) << [1, 2, 3, 4]
> > => [[1, 2, 3, 4]]
> >
> > But
> >
> >>> ( a ||= ) += [ 1, 2, 3, 4 ]
> > SyntaxError: compile error
> > (irb):28: syntax error, unexpected tOP_ASGN, expecting $end
> > ( a ||= ) += [ 1, 2, 3, 4 ]
> > ^
> > from (irb):28
> >
> > Why?
> >
> > I guess it's a precedence issue. '<<' is a method in the Array class.
> > '+=' is not.No, it's not a precedence issue. Btw, you are comparing apples and
oranges here: += and << are not equivalent (see also further below):irb(main):001:0> a=%w{foo bar}
=> ["foo", "bar"]
irb(main):002:0> b=a.dup
=> ["foo", "bar"]
irb(main):003:0> c=a.dup
=> ["foo", "bar"]
irb(main):004:0> b << a
=> ["foo", "bar", ["foo", "bar"]]
irb(main):005:0> c += a
=> ["foo", "bar", "foo", "bar"]<< adds the whole Array as one object while += "appends" the Array.
You rather want Array#concat.> The difference is that << is a method, += is an assignment. (a ||= )
> returns an object, on which you can call a method, but you can't assign
> to. You can only assign to the a variable itself, which (a ||= ) is
> not. I guess.Exactly: the expression (a||=) is not an lvalue, i.e. cannot
assigned to. But you can do( a ||= ).concat [ 1, 2, 3, 4 ]
Simon, please also keep in mind that += and << have different
semantics. += will create a new Array while << appends to the current
one.Kind regards
robert
--
Simon Mullis
_________________
simon@mullis.co.uk
That's why you should be using #concat (more efficient) unless you do
not want to modify the original array. Read the solutions properly!
Cheers
robert
2007/10/12, Simon Mullis <simon@mullis.co.uk>:
Thanks for this Robert.
The difference between the two is exactly why I wanted to use += and
not <<. I want to add many arrays to one big one and not have to use
the extra step of Array#flatten at the end.
Yep... concat it is!
Cheers!
SM
On 10/12/07, Robert Klemme <shortcutter@googlemail.com> wrote:
2007/10/12, Simon Mullis <simon@mullis.co.uk>:
> Thanks for this Robert.
>
> The difference between the two is exactly why I wanted to use += and
> not <<. I want to add many arrays to one big one and not have to use
> the extra step of Array#flatten at the end.That's why you should be using #concat (more efficient) unless you do
not want to modify the original array. Read the solutions properly!
Cheers
robert
--
Simon Mullis
_________________
simon@mullis.co.uk