Understanding Scope
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A scope is a section of code where a variable is defined, in a valid state, and the variable is visible.
e.x.
do
local x = "banana"
--| X was declared in this scope, cannot be accessed in outer scopes, but can be accessed in inner scopes.
print(x) --> banana
end
print(x) --> nil
Global VS Local Variables
A local variable has the lifetime of the scope they’re declared in and are locked to that scope and inner scopes.
A global variables lifetime is the time the script is running; it is not locked to any scope.
e.x.
do
local x = "banana" -- Local Variable
-- X's lifetime is dependent on this scope since it's declared here.
y = "apple" -- Global Variable
-- Y's lifetime is only dependent on the runtime of the script.
end
print(x) --> nil
print(y) --> apple
This applies with functions too, functions declared via local function foo() is almost like doing local foo = function() end.
e.x.
local function foo() -- function foo()
--
end -- end
-- Similar too
local foo
foo = function() -- foo = function()
--
end -- end
Nesting Scopes
do
local x = "banana"
y = "apple"
do
local z = "tomato"
t = "pear"
print(x, y, z, t) --> banana apple tomato pear
end
print(x, y, z, t) --> banana apple nil pear
end
print(x, y, z, t) --> nil apple nil pear
Shadowing
Shadowing a variable is when you redefine what the value is later down in the same scope or an inner scope and results in unwanted behavior. A reason why globals should be avoided.
e.x. You have a variable x and you define another one in a different scope y, but you named it x instead.
local x = "banana"
do
local x = "apple"
print(x, y) --> apple (expected banana) nil (expected apple - shadowed outer variable `x`)
end
print(x) --> banana