Hey all,
If I have a string like “Math”, I know I can use const_get to turn it
into
an instance of Class. Awesome.
But what if I have something like “Math::PI”. Am I stuck using eval to
resolve that?
On 27.08.2010 17:24, Andrew W. wrote:
If I have a string like “Math”, I know I can use const_get to turn it into
an instance of Class. Awesome.But what if I have something like “Math::PI”. Am I stuck using eval to
resolve that?
One typical idiom looks like this:
a_class = str.split(’::’).inject(Object) {|cl,n| cl.const_get n}
Cheers
robert
Well, sure. That’s a good point. But now you’re taking 3 times as long
as
eval, instead of 1/5 the time, according to my tests.
On Fri, Aug 27, 2010 at 11:40 AM, Robert K.
Err, I think I wasn’t very clear in my last email, so I’ll say it in a
benchmark this time.
require ‘benchmark’
Benchmark.bm do |b|
b.report “using eval” do
1_000_000.times { eval “Math” }
end
b.report “using const_get” do
1_000_000.times { Kernel.const_get “Math” }
end
b.report “using eval on Math::PI” do
1_000_000.times { eval “Math::Pi” }
end
b.report “using const_get injection on Math::PI” do
1_000_000.times { “Math::PI”.split("::").inject(Object) { |cl,n|
cl.const_get n } }
end
end
using eval 6.5
using const_get 1.297
using eval on Math::Pi 6.875
using const_get injection on Math::PI 18.65
Without the performance benefit, it seems like there’s not much benefit
in
avoiding eval :(.
On Fri, Aug 27, 2010 at 10:40 AM, Robert K.
[email protected]wrote:
Here is how Rails implements Robert’s suggestion:
(see method constantize)
Please do not top post.
On 27.08.2010 17:48, Andrew W. wrote:
Well, sure. That’s a good point. But now you’re taking 3 times as long as
eval, instead of 1/5 the time, according to my tests.
Is it a performance issue? If not, why bother now? The version with
eval is much less secure plus eval might not work under all
circumstances with your string (see $SAFE).
Cheers
robert