blog - How to Concatenate Strings in Lua

benchmark.sh

hyperfine 'lua slow.lua'
# Benchmark #1: lua slow.lua
#   Time (mean ± σ):      1.287 s ±  0.115 s    [User: 1.120 s, System: 0.078 s]
#   Range (min … max):    1.187 s …  1.528 s    10 runs
hyperfine 'lua fast.lua'
# Benchmark #1: lua fast.lua
#   Time (mean ± σ):      39.3 ms ±   3.8 ms    [User: 34.6 ms, System: 2.8 ms]
#   Range (min … max):    35.3 ms …  58.3 ms    48 runs

concatenation-operator.lua

message = "Hello, " .. "world!"
-- message equals "Hello, World!"

direct-approach.lua

for i=1,100000 do
  io.stdout:write(i)
end

immutable-strings.lua

start = "Hello, "
message = start .. "world!"
start = "Bye, "
-- message still equals "Hello, World!"

many-concatenations.lua

message = ""
for i=1,100000 do
  message = message .. i
end

no-augmented-assignment.lua

message = "Hello, "
message ..= "world!"
-- results in a "syntax error near '..'" error

number-coercion.lua

count = 42
message = "The count is: " .. count
-- message equals "The count is: 42"

separator-argument.lua

message = table.concat({1, 2, 3, 4, 5})
-- message equals "12345"
message = table.concat({1, 2, 3, 4, 5}, ", ")
-- message equals "1, 2, 3, 4, 5"

start-and-end-indexes.lua

message = table.concat({1, 2, 3, 4, 5}, ", ", 2, 4)
-- message equals "2, 3, 4"

table-concat.lua

numbers = {}
for i=1,100000 do
  numbers[i] = i
end
message = table.concat(numbers)

type-error.lua

count = nil
message = "The count is: " .. count
-- results in an "attempt to concatenate a nil value" error