Create named objects

R

Roland Schmitt

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
 
K

kgoblin

Roland said:
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 )
 
D

dblack

Hi --

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 :)

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

--
David A. Black ([email protected])
Ruby Power and Light (http://www.rubypowerandlight.com)

"Ruby for Rails" chapters now available
from Manning Early Access Program! http://www.manning.com/books/black
 
L

Logan Capaldo

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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 )

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.
--Apple-Mail-13--275638156--
 

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