Anyone can help me on this ?

Hi there.

I had a lot of fun with this Kata, but I'm a bit stuck with one of the test : the one on Glider4.

It expects
░░░░░░░░░░░
░░░░░░░░░░░
░░░░░░░░░░░
░░░░░░░░░░░
░░░░▓░░░░░░
░░░░░▓▓░░░░
░░░░▓▓░░░░░
░░░░░░░░░░░
░░░░░░░░░░░
░░░░░░░░░░░
░░░░░░░░░░░

But in the instructions, it's said that the result must be "cropped around all of the living cells".
I'm a bit frustrated because my implementation returned
▓░░
░▓▓
▓▓░

which contains the expected living cells.

I'm not a native english speaker (as you probably already guess), and I may have misunderstood the instructions.

Very concise, I've never think to use splat in invokation to replace a concat.

You can avoid the dot when using @ : @.before is equivalent to @before

Hello ! you should give a comprehensive comment, I think this should be promoted to best practice.