Concatenating strings

Lua:
Concatenating strings

How to:

In Lua, you concatenate strings with the .. operator. Let’s see it in action:

local hello = "Hello, "
local world = "world!"
local greeting = hello .. world

print(greeting)  -- Output: Hello, world!

You can even tack on numbers with a little coercion:

local base = "I have "
local itemCount = 3
local message = base .. itemCount .. " apples"

print(message)  -- Output: I have 3 apples

Remember, conversion of non-string types is manual:

local score = 9001
local displayScore = "Your score is: " .. tostring(score)

print(displayScore)  -- Output: Your score is: 9001

Deep Dive

String concatenation might seem mundane, but it’s vital. In Lua’s early days, it was intended for embedded systems, which meant keeping things light. That’s why .. was chosen for strings - it’s simple yet effective.

Alternatives to .. include:

table.concat function for arrays of strings, more efficient for concatenating many strings.
String library functions like string.format, offering more control over formatting.

Lua’s string concatenation performance was a concern, specifically with .. because each use creates a new string, which can be costly in loops. To mitigate this, when concatenating in a loop, use tables:

local parts = {}
for i = 1, 10 do
    parts[i] = "Part " .. i
end
local combined = table.concat(parts, ", ")

print(combined)  -- Output: Part 1, Part 2, ... Part 10

Internally, Lua manages strings in a hash table to optimize memory usage, so identical strings share the same storage. But, concatenation breaks this sharing because of the new strings it creates.

Lua:Concatenating strings

How to:

Deep Dive

See Also

Lua:
Concatenating strings