While it's poweful in its "meta-programming" facilities and has some nicities, it has many uneeded bizarro decisions.
This alone was enough to make me leave it:
http://stackoverflow.com/questions/2705793/how-to-get-number...
num_items = #my_array
In C++, what operator tells you how many instance variables a class has? There is none, because that wouldn't make sense in many use cases. Lua tables, offering prototype-based inheritance, experience a similar conceptual ambiguity in the case where you want to take the length of an object.
Lua has made a design decision that the built-in length operator only works on arrays = tables-used-as-a-list and on strings -- cases without ambiguity. If you want the length operator to make sense for a hash map usage, it's a few extra lines of work for you. It's consistent with the langauge being small and flexible, a theme which Lua embraces with elegance.
My qualms are multiple:
(a) this is an operator when it doesn't need to -- a function would do --,
(b) this only works for contiguous list of items.
(c) Lua, like PHP and JS, has the same type for "contiguous list of items" and hash tables, not even providing a builtin just for the first and/or the latter (e.g. ES6 now does with "Map").
I can understand the powerful metaprogramming capabilities of tables. I also understand that they are not needed, and are even a hidrance, in the tons of cases where all you want is a simple hashmap or a simple vector that wont change under your feet.
>* In C++, what operator tells you how many instance variables a class has?*
Nobody said C++ was well designed ever, too.
I somewhat agree, though it hasn't stopped me from using it extensively. The example that you give isn't a very good one, it makes more and more sense as you get to understand the language.
However: 1-indexed arrays; and words as block delimiters ("end end end end...") are things that make me regularly take a step back and think, this would be a bit nicer if the language did things the normal way. Note that 1-indexed arrays are especially annoying in LuaJIT because the FFI naturally encourages you to manipulate C arrays, often resulting in a mix of 0-indexed and 1-indexed arrays. Ouch.