Why use ipairs and not just #?

[noatom]

So ipairs is mostly used like this:
for i,v in ipairs(t) do print(i,v) end

Why not just do this?
for i,#t do print(i,v) end

[Boolsheet]

That's not valid Lua. You would have to do this.

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for i = 1, #t do
    print(i, t[i])
end

It's mostly for convenience and readability.

[noatom]

what about:

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t = { apple="green", orange="orange", banana="yellow" }
for k,v in pairs(t) do print(k,v) end

is there an alternative to pairs? like above?

[bartbes]

Short version: Not really.
Long version:

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do
  local k, v = next(t)
  while k do
    --stuff
    k, v = next(t, k)
  end
end

[Taehl]

Numeric for is faster than ipairs, so I'd suggest using it in time-critical code (ie., inside love.update and love.draw), but elsewhere, ipairs is fine.

[Xgoff]

plus, ipairs and a numeric loop using # behave differently: ipairs will stop at the first nil, # will stop at whichever nil it wants (the typical problem it has with holes)

[Taehl]

Are you sure about that, Xgoff? I use #table all the time, and have never had any behavior like that. I thought that ipairs always behaved exactly the same as #table in regards to sequential numeric indices and nils.

[Boolsheet]

Yes, that is correct. The Lua manual states that the length operator can ignore such holes in the sequence. An example:

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print( #{1, nil, 3} ) -- May print 3

This can vary with the implementation. LuaJIT behaves differently here.

[master both]

maybe, he were talking about this type of holes .
ps:boolsheet, great web page.