How to do: var1 = var2.new(.....) (var2 contains classname)

ruby-talk
1

Hi All

I have a situation in which I have the name of the class in a variable
So normally I would do
    song = Song.new("Bicylops", "Fleck", 260)

But I need to do something like
    var2 = "Song"
    var1 = var2.new("Bicylops", "Fleck", 260)

This doesn't work!
Any suggestions how to do this ?

Thnx
LuCa

···

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2

var1 = Object.get_const(var2).new("Bicyclops", "Fleck", 260)

···

On 2/14/07, Luca Scaljery <lcalje@gmail.com> wrote:

I have a situation in which I have the name of the class in a variable
So normally I would do
    song = Song.new("Bicylops", "Fleck", 260)

But I need to do something like
    var2 = "Song"
    var1 = var2.new("Bicylops", "Fleck", 260)

This doesn't work!
Any suggestions how to do this ?

3

You need to convert your string "Song" into a Class object.

var2 = "Song"
var1 = Object.const_get(var2).new("Bicyclops", "Fleck", 260)

All class and module objects are stored as constants in Object. It
gets a little tricky if you have a class withing a module --
"Music::Song". Then you'll have to do something like this:

current = Object
var2 = "Music::Song"
var2.split("::").each do |str|
  current = current.const_get(str)
end
var1 = current.new( ... )

Hope this helps

TwP

···

On 2/14/07, Luca Scaljery <lcalje@gmail.com> wrote:

Hi All

I have a situation in which I have the name of the class in a variable
So normally I would do
    song = Song.new("Bicylops", "Fleck", 260)

But I need to do something like
    var2 = "Song"
    var1 = var2.new("Bicylops", "Fleck", 260)

This doesn't work!
Any suggestions how to do this ?

4

Maybe you want to have a look at this:

var1 = Object.const_get(var2)

Kind regards
Nicolai

···

2007/2/14, Luca Scaljery <lcalje@gmail.com>:

Hi All

I have a situation in which I have the name of the class in a variable
So normally I would do
    song = Song.new("Bicylops", "Fleck", 260)

But I need to do something like
    var2 = "Song"
    var1 = var2.new("Bicylops", "Fleck", 260)

This doesn't work!
Any suggestions how to do this ?

Thnx
LuCa

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Posted via http://www.ruby-forum.com/\.

5

Hi

Thanks for the solution!
It works!!

LuCa

···

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6

Luca Scaljery <lcalje <at> gmail.com> writes:

Hi All

I have a situation in which I have the name of the class in a variable
So normally I would do
    song = Song.new("Bicylops", "Fleck", 260)

I'm surprised no one else has mentioned this, but there's very little need to
store a class name in a string. Usually if you're doing this then there's
something wrong with your methodology and there's a much more efficient way to
get the right results.

The only real reason I can think that you'd have that in a string and not simple
as the class constant is if you took it from user input. Hopefully you aren't
letting your users decide which classes get instantiated..!

7

Whoops, that should be "const_get(var2)", not "get_const(var2)".

···

On 2/14/07, Lyle Johnson <lyle.johnson@gmail.com> wrote:

var1 = Object.get_const(var2).new("Bicyclops", "Fleck", 260)

8

Lyle Johnson wrote:

var1 = Object.get_const(var2).new("Bicyclops", "Fleck", 260)

should be #const_get()

···

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