Lua by Example: Methods

lua supports methods defined on tables.

items declared in this table are shared between all instances but can be overridden

 
local My_Psuedo_Class = {
    shared = "string is shared"
}
 
function My_Psuedo_Class:new()

items declared in this table are unique between instances

 
    local instance = {
        unique = "string is unique"
    }
 
    setmetatable(instance, { __index = My_Psuedo_Class })
 
    return instance
end

declaration of a method that changes internal state

 
function My_Psuedo_Class:method(new_val)
    self.shared = new_val
    self.unique = new_val
end

another method that prints internal state

 
function My_Psuedo_Class:print()
    print('shared: ', self.shared, ' unique: '..self.unique)
end
 
local instance_a = My_Psuedo_Class:new()
local instance_b = My_Psuedo_Class:new()
 
instance_a:print()
instance_b:print()
print()

we can change the shared state

 
My_Psuedo_Class.shared = "new shared state"
 
instance_a:print()
instance_b:print()
print()
 
instance_a:method('overwrite first')
instance_b:method('overwrite second')
 
instance_a:print()
instance_b:print()
print()

once the members have overridden the shared state changes will only affect new instances

 
My_Psuedo_Class.shared = "only in inst. c"
local instance_c = My_Psuedo_Class:new()
 
instance_a:print()
instance_b:print()
instance_c:print()
 
$ lua methods.lua
shared:     string is shared     unique: string is unique
shared:     string is shared     unique: string is unique
 
shared:     new shared state     unique: string is unique
shared:     new shared state     unique: string is unique
 
shared:     overwrite first     unique: overwrite first
shared:     overwrite second     unique: overwrite second
 
shared:     overwrite first     unique: overwrite first
shared:     overwrite second     unique: overwrite second
shared:     only in inst. c     unique: string is unique

Next example: JSON and Library Loading.

by Blake Bourque | source | license