>ruby eval_bench.rb
                user     system      total        real
eval:       1.141000   0.000000   1.141000 (  1.156000)
const_get:  0.156000   0.000000   0.156000 (  0.172000)

>cat eval_bench.rb
require 'benchmark'
class Foo;end
some_class = 'Foo'
Benchmark.bm(10) do |b|
  b.report("eval:") { 100000.times {eval("#{some_class}.new")} }
  b.report("const_get:") { 100000.times{Object.const_get(some_class).new} }
end

On 5/4/06, Charlie Bowman <charlie / castlebranch.com> wrote:
> I understand the ugliness of eval....but why shouldn't we use it?  It is
> much quicker to write, shorter to read, and easier to use.
>
> On Fri, 2006-05-05 at 04:19 +0900, Patrick Hurley wrote:
>
> > On 5/4/06, Patrick Hurley <phurley / gmail.com> wrote:
> > > On 5/4/06, Gregory Seidman <gsslist+ruby / anthropohedron.net> wrote:
> > > > On Fri, May 05, 2006 at 03:51:39AM +0900, RGR wrote:
> > > > } I want to create an object from a class, but the name of that class is
> > > > } in a variable, so the form obj=Class.new(args) can't be used. How can it
> > > > } be done? Without using eval, because its a bit messy and unelegant.
> > > > }
> > > > } The equivalent of obj=$variable_with_class_name(args) in php.
> > > >
> > > > obj = Object::const_get(class_name).new(args)
> > > >
> > > > } Thanks.
> > > > } RGR
> > > > --Greg
> > > >
> > > >
> > > >
> > >
> > > And if args is an array you want to use as individual params:
> > >
> > > obj = Module.const_get(class_name).new(*args)
> > >
> > > (note I prefer Module. but both work)
> > > pth
> > >
> >
> > Ara is of course correct, so you end up with something like:
> >
> > klass = var_with_class.to_s.split('::').inject(Module) { |base,klass|
> > base.const_get(klass) }
> > obj = klass.new(*args)
> >
> > If this is a common operation in your code, you could add this into
> > Module or some other reasonable place.
> >
> > pth
> >
> >
>
>
>
>