"val.dup rescue val" sloooow

[Michael Neumann]

Hi,

I just wanted to tell you that if you do

val.dup rescue val

somewhere in your program, you should probably switch to:

case val
when Fixnum, nil, true, false
# non dup-able
val
else
val.dup rescue val
end

which is much faster if you have lots of non-dupable values.

Regards,

Michael

 

[Robert Klemme]

Hi,

I just wanted to tell you that if you do

val.dup rescue val

somewhere in your program, you should probably switch to:

case val
when Fixnum, nil, true, false
# non dup-able
val
else
val.dup rescue val
end

which is much faster if you have lots of non-dupable values.

While that works and is efficient, I'd prefer any of these two solutions:

- Remove #dup from types that can't be duped, so we can check with
respond_to?

- Have #dup return self in these cases (immutable instances anyway).

I'm not sure though which negative implications the second approach could
have. From a usage point of view I'd certainly prefer it. I remember
this came up before and I think Matz opted for the first solution:
http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/32556

Kind regards

robert

 

[Michael Neumann]

While that works and is efficient, I'd prefer any of these two solutions:

- Remove #dup from types that can't be duped, so we can check with
respond_to?

- Have #dup return self in these cases (immutable instances anyway).

Yes that seems reasonable, as e.g. #freeze does not raise an error on
these kind of objects, too.

Regards,

Michael