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delegator

cp.delegator is a middleclass "mix-in" that allows for simple specification of "delegated" values and functions in class definitions.
This allows you to compose an object from other objects, but allow methods or values from the composed values to be accessed directly via the composing parent object.
For example:
local class = require "middleclass"
local delegator = require "cp.delegator"
local Minion = class("Minion")
function Minion:doTask()
-- does something...
return true
end
local Boss = class("Boss"):include(delegator):delegateTo("minion")
function Boss:initialize()
end
function Boss:hireMinion(minion)
self.minion = minion
end
local johnSmith = Boss()
local joeBloggs = Minion()
johnSmith:doTask() -- error: no 'doTask' method available.
johnSmith:hireMinion(minion)
johnSmith:doTask() -- can now do the task, because his minion does it for him.
johnSmith.minion:doTask() -- The exact same thing.
The order that delegator is included with other mixins can affect how it functions. For example, when mixing with cp.lazy, if cp.lazy is mixed in second, like so:
local MyClass = class("MyClass"):include(delegator):include(lazy):delegateTo("delegate")
function MyClass:initialize()
self.delegate = {
value = "delegated value"
}
end
function MyClass.lazy.value()
return "lazy value"
end
local myInstance = MyClass()
assert(myInstance.value == "delegated value") -- passes
assert(myInstance.delegated.value == "delegated value") -- passes
...then any delegated methods will take priority over lazy ones. Most likely you want to put lazy first, like so:
local MyClass = class("MyClass"):include(lazy):include(delegator):delegateTo("delegate")
function MyClass:initialize()
self.delegate = {
value = "delegated value"
}
end
function MyClass.lazy.value()
return "lazy value"
end
local myInstance = MyClass()
assert(myInstance.value == "lazy value") -- passes
assert(myInstance.delegated.value == "delegated value") -- passes
The easy way to remember is to read them together - "lazy delegator" sounds better than "delegator lazy".

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