$a = 5; $b = 'a'; print $$b

ruby-talk
1

Hello,

I’m a seasoned Perl programmer trying to learn Ruby.

Is there a way a variable name can be variable? Like, how would I
rewrite the following piece of Perl code in Ruby:

$a = 5;
$b = 'a';
print $$b; # should print 5

And can this be done with instance variables? I’m trying to do this:

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
@(key) = vals[key] # This doesn’t work; syntax error
}
end
end

s = Series.new({“sid” => 3, “handle” => “smoon”, “name” => “Sailor Moon”})
puts s.name # should print “Sailor Moon”

2

Hello,

I’m a seasoned Perl programmer trying to learn Ruby.

Is there a way a variable name can be variable? Like, how would I
rewrite the following piece of Perl code in Ruby:

$a = 5;
$b = ‘a’;
print $$b; # should print 5

a = 5
b = ‘a’
puts eval b

And can this be done with instance variables? I’m trying to do this:

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
@(key) = vals[key] # This doesn’t work; syntax error

I don’t understand what you are trying to do here.

/Erik

···

On Mon, 2002-06-03 at 00:49, Philip Mak wrote:

–
Erik Bågfors | erik@bagfors.nu
Supporter of free software | GSM +46 733 279 273
fingerprint: 6666 A85B 95D3 D26B 296B 6C60 4F32 2C0B 693D 6E32

3

Philip Mak pmak@animeglobe.com writes:

And can this be done with instance variables? I’m trying to do this:

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
@(key) = vals[key] # This doesn’t work; syntax error
}
end
end
This particular case can be rewritten either with instance_eval or
method_missing. Which is less evil is up to you.

% cat series_eval.rb
class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
instance_eval “@#{key} = vals[key]”
}
end
end

s = Series.new({“sid” => 3, “handle” => “smoon”, “name” => “Sailor Moon”})
puts s.name # should print “Sailor Moon”
%

% ruby series_eval.rb
Sailor Moon

% cat series_missing.rb
class Series
def initialize(vals)
@vals = vals
end

def method_missing (symbol, *args)
@vals[symbol.to_s]
end
end

s = Series.new({“sid” => 3, “handle” => “smoon”, “name” => “Sailor Moon”})
puts s.name # should print “Sailor Moon”
%

% ruby series_missing.rb
Sailor Moon
%

– Ed

4

Basically, I want to do this:

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
@sid = vals[‘sid’]
@handle = vals[‘handle’]
@name = vals[‘name’]
end
end

without having to type out the @x = vals[‘x’] line for each and every
instance variable, since I have other classes that have a lot of
variables.

I tried eval(@key = vals[key]) and eval(@key) = vals[key] but those
didn’t evaluate correctly.

···

On Mon, Jun 03, 2002 at 07:57:43AM +0900, Erik Bågfors wrote:

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
@(key) = vals[key] # This doesn’t work; syntax error

I don’t understand what you are trying to do here.

5

I think I got it.

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
eval(“@” + key + “= vals[key]”)
}
end
end

A bit kludgy looking (I’m porting something from Perl, and it abused
the fact that classes are hashes in Perl) but it works.

···

On Mon, Jun 03, 2002 at 08:08:29AM +0900, Philip Mak wrote:

I tried eval(@key = vals[key]) and eval(@key) = vals[key] but those
didn’t evaluate correctly.

6

Hi,

class Series
attr_accessor :sid, :handle, :name
def initialize(vals)
vals.each_key { |key|
eval(“@” + key + “= vals[key]”)
}
end
end

A bit kludgy looking (I’m porting something from Perl, and it abused
the fact that classes are hashes in Perl) but it works.

Series = Struct.new(nil, :sid, :handle, :name)
class Series
def initialize(vals)
super(*vals.indexes(*members))
# super(*vals.select(*members)) # for 1.7
end
end
a = Series.new(“sid”=>3, “handle” => “smoon”, “name” => “Sailor Moon”)
puts a.name

···

At Mon, 3 Jun 2002 08:27:04 +0900, Philip Mak wrote:

–
Nobu Nakada