[elif]

>I don’t think there’s any language, interpreted or otherwise, with the goal that knowing its internals won’t help you gain more performance.

It is, indeed, a fundamental goal of ruby that there are multiple ways to write the same thing, and that the programmer should not need to understand nuances of the compiler.

"I need to guess how the compiler works. If I'm right, and I'm smart enough, it's no problem. But if I'm not smart enough, and I'm really not, it causes confusion. The result will be unexpected for an ordinary person. This is an example of how orthogonality is bad." -matz 2003.

[wrs]

That's about semantics, not performance. I don't think Matz would say that a goal of Ruby is to prevent you from improving performance using whatever knowledge you do have about the compiler.

In this particular example, the fact that assignments return the value of the right-hand side is well-known and used frequently in Ruby code. The fact that arrays have to be allocated is obvious. The fact that allocations have a runtime cost is obvious. The only thing that isn't obvious is that the return value allocation of assignments whose value isn't used are optimized away. If you know that, you'll think of appending the nil to activate that optimization. Characterizing the lack of that step as a "mistake" only makes sense if the goal for your code is to maximize performance -- which in this case, most unusually for Ruby, it was.