Is

Returns whether a value is, or inherits from, a class or type.

Built initially for LÖVE2D, this helper function easily checks standard Lua types, LÖVE Objects, or Classy Objects. It may also unitentonally handle other classes, you mileage may vary.

Usage

--Standard lua type
local a = 5

is(a, "number") -- true

--LÖVE type
local b = love.physics.newWorld(0, 9.12, false)

--LÖVE types are case sensitive
--They are userdata, and due to
--order of operations, so will
--also return true for "userdata"
is(b, "world")    -- false
is(b, "World")    -- true
is(b, "userdata") -- true

--Classy type
local c = Point(10, 20)

--Classy compares against the Class
--object directly, so name comparisons
--will always return false.
is(c, "Point") -- false
is(c, Point)   -- true

--Classy's is method checks inheritence.
is(c, Object) -- true

--If extended_types has been added to the
--project, then Classy types will NOT be
--read as a table. If extended_types is
--not part of the project, then it WILL
--be read as a table.

--With extended_types:
is(c, "table") -- false

--Without extended_types:
is(c, "table") -- true

In order, it checks the following;

• If the value's type() is one of the standard lua types, compare it to the passed class. Lua's standard types don't inherit, so this is equivalent to type(value) == Class
• If the value's type() is userdata, attempt to call the .typeOf method of the userdata. This is to compare against LÖVE types.
• Finally, attempt's to call the .is method of whatever's left. This will handle Classy classes. If using extended_types, then this function will work as expected, otherwise, Classy classes will read as tables and will pretty much always return false.