LUA: null coalescing ??

[ArithEU]

Hey there

I'm very inexperienced with Lua (I'm a C# developer) and I was wondering if there's a null coalescing operator I could use to handle any null/empty strings?

for example in C# I would do

string a = b ?? c;

which would give a the value of c if b was null.

[TOM_RUS]

Something like this:

local a = nil
local b = "123"
local c = a or b
print(c)

should assign "123" to c.

But if a is "", then it won't work.

[semlar]

If you want to check that the variable both exists and is not an empty string, you could do something like this

local a = (b and b ~= '') and b or c

This is called short-circuiting and it stops when the condition evaluates to true.

The above is equivalent to writing

local a
if b and b ~= '' then
  a = b
else
  a = c
end

[Phanx]

Also, for the purposes of simple "if x then" checks in Lua, a value of false is the same as "not existing" or having a value of nil.

a = b or c

... is the same as:

a = (b ~= nil and b ~= false) and b or c

... which is the same as :

if b ~= nil and b ~= false then
    a = b
else
    a = c
end

... so if you need to distinguish between a boolean false and an actual nil value, you'll have to explicitly check.