Closures in Lua

A function captures the locals around it, alive between calls.

-- A closure captures the locals around it, alive between calls.
local function make_counter(label)
  local seen = 0
  return function()
    seen = seen + 1
    return label .. " #" .. seen
  end
end

local kills = make_counter("skeleton")
local finds = make_counter("relic")

print(kills())
print(kills())
print(finds())
print(kills())

How it works

make_counter returns a function still holding seen.
Each returned counter owns its own upvalue.
Calls interleave without crosstalk between the two.

Keywords and builtins used here

end
finds
function
kills
local
make_counter
print
return

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Step 1 of 3 in Closures, step 14 of 27 in Language basics.

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Closures in other languages