What does # mean in Lua?

Question

I have seen the hash character '#' being added to the front of variables a lot in Lua.

What does it do?

EXAMPLE

-- sort AIs in currentlevel table.sort(level.ais, function(a,b) return a.y < b.y end) local curAIIndex = 1 local maxAIIndex = #level.ais for i = 1,#currentLevel+maxAIIndex do     if level.ais[curAIIndex].y+sprites.monster:getHeight() < currentLevel[i].lowerY then         table.insert(currentLevel, i, level.ais[curAIIndex])         curAIIndex = curAIIndex + 1         if curAIIndex > maxAIIndex then             break         end     end end 

Apologies if this has already been asked, I've searched around on the internet a lot but I haven't seem to have found an answer. Thanks in advance!

Answer 1

That is the length operator:

The length operator is denoted by the unary operator #. The length of a string is its number of bytes (that is, the usual meaning of string length when each character is one byte).

The length of a table t is defined to be any integer index n such that t[n] is not nil and t[n+1] is nil; moreover, if t[1] is nil, n can be zero. For a regular array, with non-nil values from 1 to a given n, its length is exactly that n, the index of its last value. If the array has "holes" (that is, nil values between other non-nil values), then #t can be any of the indices that directly precedes a nil value (that is, it may consider any such nil value as the end of the array).