operators.md

Operators

Self-assignment operators

Lunar adds 7 new operators for self-assignment operators: ..=, +=, -=, *=, /=, ^=, and %=.

These type of self-assignment operators are applicable to the same syntax you use to assign to local (not declaring!) or global variables.

These are all legal.

local a, b = 1, 2
a, b += 1, 2 --> a = 2, b = 4

We do not discard extra expressions so if you intended to have side effects while self-assigning to a variable, it's as easy as...

local c = 3
c += 4, 5 --> c = 7, and 5 is assigned to nothing

local function some_number(n)
  print(n)
  return n
end

local d = 4
d += 5, some_number(6) --> d = 9, some_number is called and prints 6

We have a special case where if you have too many members and too few expressions, it will emit invalid Lua. This is intentional!

These will throw an error at run time. Eventually this will be caught at compile time, but currently this is a good way of dealing with too many members.

local a, b = 1, 2
a, b += 1

-- That would emit the following...
a, b = a + 1, b + nil -- ack! using + operator on a nil value is an error!