Create named objects

ruby-talk
1

Hello,

want to do the following:

name = "input"
clazz = "String"
value = "test"

<<<some magic here>>>

puts(input) -> "test"
input.class() -> String

Thanks in advance,

Roland

2

Roland Schmitt wrote:

Hello,

want to do the following:

name = "input"
clazz = "String"
value = "test"

<<<some magic here>>>

puts(input) -> "test"
input.class() -> String

Thanks in advance,

Roland

a pretty straight forward way is to just use the eval function on a
string

# in your insert magic here:
evs = "#{name} = #{clazz}.new( #{value} )"
eval( evs )

3

Hi --

Roland Schmitt wrote:

Hello,

want to do the following:

name = "input"
clazz = "String"
value = "test"

<<<some magic here>>>

puts(input) -> "test"
input.class() -> String

Thanks in advance,

Roland

a pretty straight forward way is to just use the eval function on a
string

# in your insert magic here:
evs = "#{name} = #{clazz}.new( #{value} )"
eval( evs )

That will create a new inner scope, so if there's no variable named
input already, there won't be one when the eval exits. (Which is
good, because otherwise we'd probably be seeing a lot of this kind of
thing :slight_smile:

The best advice, though it's not exactly an answer to the question,
is: use a hash.

   name = "input"
   value = "test"
   value_hash[name] = test

rather than the "soft reference"-style (to borrow a Perl phrase) way
of creating locals.

David

···

On Thu, 2 Mar 2006, kgoblin@gmail.com wrote:

--
David A. Black (dblack@wobblini.net)
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! Ruby for Rails

4

alternatively:

name = "input"
clazz = "String"
value = "test"

(class << self; self; end).class_eval { define_method(name) { const_get(clazz).new(value) } }

puts(input)
puts input.class

There are several disadvantages to this approach.
1) input is a method not really a variable and therefore its scope is gonna be all sorts of wrong
2) Since it is a method, assigning to it is not necessarily going to work the way you want

Advantages ares that yo don't have to worry about the having seen an assignment to it business and you don't have to invoke the parser

Yet another method would be
instance_variable_set("@#{name}", Object.const_get(clazz).new(value))

Unfortunately now you have to refer to it as @input. It also has some scoping issues.

···

On Mar 1, 2006, at 11:33 AM, kgoblin@gmail.com wrote:

Roland Schmitt wrote:

Hello,

want to do the following:

name = "input"
clazz = "String"
value = "test"

<<<some magic here>>>

puts(input) -> "test"
input.class() -> String

Thanks in advance,

Roland

a pretty straight forward way is to just use the eval function on a
string

# in your insert magic here:
evs = "#{name} = #{clazz}.new( #{value} )"
eval( evs )