Use a string a object name

ruby-talk
1

Hi.

I've a little problem. How can I use a string use as an object name?

That works well:
puts p.name # -> dirk

But how can I use the string s as object name, I tried eval but I the result is not good. Where is my mistake. Can anybody help me?

s = 'name'
puts eval "p.s"

greetings
Dirk Einecke

2

Did you mean,
puts eval "p s" # => "name"

···

--- Dirk Einecke <dirk.einecke@gmx.de> wrote:

Hi.

I've a little problem. How can I use a string use as an object name?

That works well:
puts p.name # -> dirk

But how can I use the string s as object name, I tried eval but I the
result is not good. Where is my mistake. Can anybody help me?

s = 'name'
puts eval "p.s"

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3

Dirk Einecke wrote:

Hi.

I've a little problem. How can I use a string use as an object name?

That works well:
puts p.name # -> dirk

But how can I use the string s as object name, I tried eval but I the result is not good. Where is my mistake. Can anybody help me?

s = 'name'
puts eval "p.s"

since you want to put the value of s into the string that get's evaled you need to enclose it in #{ } like this

puts eval "p.#{s}"

Though depending on what you're doing a better way might be to use the send method

puts p.send(s)

···

--
Mark Sparshatt

4

puts eval "p.#{s}"

···

On Sun, 13 Jun 2004 21:31:27 +0200, Dirk Einecke wrote:

I've a little problem. How can I use a string use as an object name?

That works well:
puts p.name # -> dirk

But how can I use the string s as object name, I tried eval but I the
result is not good. Where is my mistake. Can anybody help me?

s = 'name'
puts eval "p.s"

--
Marek Janukowicz

5

Jeff Mitchell wrote:

Did you mean,
puts eval "p s" # => "name"

Not really...
Okay. From the scratch. I've a class to map a get params to local vars:

class CgiParamsToLocal
   def initialize(params)
     @params = params
   end
   def method_missing(m, *other)
     @params[m.to_s][0]
   end
end

p = CgiParamsToLocal.new($cgi.params)

Now I try to use a string as a object name like I wrote in my first posting.

greetings
Dirk Einecke

6

Marek Janukowicz wrote:

···

On Sun, 13 Jun 2004 21:31:27 +0200, Dirk Einecke wrote:

I've a little problem. How can I use a string use as an object name?

That works well:
puts p.name # -> dirk

But how can I use the string s as object name, I tried eval but I the result is not good. Where is my mistake. Can anybody help me?

s = 'name'
puts eval "p.s"

puts eval "p.#{s}"

The 'send' method (as Mark said) is the better way
to do this.

Hal

7

Hi.

Marek Janukowicz wrote:

puts eval "p.#{s}"

Okay. That works.

greetings
Dirk Einecke

8

Mark Sparshatt wrote:

puts eval "p.#{s}"

Okay. That works.

Though depending on what you're doing a better way might be to use the send method

puts p.send(s)

Why is this a better way?

greetings
Dirk Einecke

9

Dirk Einecke wrote:

Mark Sparshatt wrote:

puts eval "p.#{s}"

Okay. That works.

Though depending on what you're doing a better way might be to use the send method

puts p.send(s)

Why is this a better way?

It's quicker since Ruby doesn't need to parse the expression string.

Also, IMHO, it better expresses the fact that you're sending the message contained in s to the object p.

···

--
Mark Sparshatt

10

Mark Sparshatt wrote:

Dirk Einecke wrote:

Mark Sparshatt wrote:

puts eval "p.#{s}"

Okay. That works.

Though depending on what you're doing a better way might be to use the send method

puts p.send(s)

Why is this a better way?

It's quicker since Ruby doesn't need to parse the expression string.

Also, IMHO, it better expresses the fact that you're sending the message contained in s to the object p.

I forgot to mention there are using security concerns with using eval. If s is taken from an external source then it's possible for someone to set it to

"send('system', 'rm -rf /')"

which would very quickly ruin your day.

···

--
Mark Sparshatt