81 lines
2.1 KiB
Markdown
81 lines
2.1 KiB
Markdown
# Property Accessors Mixin [](https://travis-ci.org/atom/property-accessors)
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A mixin for defining dynamic properties.
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## Basic Usage
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To define a basic property accessor, use the `accessor` declaration. If you've
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included the mixin into a class, you define a prototype property by calling
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`@::accessor` on its prototype.
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```coffee
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PropertyAccessors = require 'property-accessors'
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class Vehicle
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PropertyAccessors.includeInto(this)
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@::accessor 'type',
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get: ->
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switch @doorCount
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when 4 then 'sedan' # i know this isn't strictly accurate
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when 2 then 'coupe'
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set: (type) ->
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switch type
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when 'sedan' then @doorCount = 4
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when 'coupe' then @doorCount = 2
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car = new Vehicle
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car.doorCount = 2
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car.type # => 'coupe'
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```
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You can define a class-level property by *extending* with the mixin rather than
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including it (which extends the prototype).
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```coffee
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class Vehicle
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PropertyAccessors.extend(this)
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@accessor 'vehicleCount', get: -> @allVehicles.length
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```
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You can just pass a single function if you only want to define a getter:
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```coffee
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class Vehicle
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PropertyAccessors.includeInto(this)
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@::accessor 'type', -> # ...
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```
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## Fancy Usage
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### Lazy Accessors
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Lazy accessors call a function the first time a property is accessed. You are
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still free to overwrite this value by assigning the property explicitly.
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```coffee
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class ScienceLab
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PropertyAccessors.includeInto(this)
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@::lazyAccessor 'crazyComputation', -> computeCrazyComputation()
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```
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### Advised Accessors
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Advised accessors allow you to call code before the reading or writing of a
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property value. If a property is being assigned, your advice function is called
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with the value being assigned and the old value.
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```coffee
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class SpyStation
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@advisedAccessor 'online',
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get: -> @ensureAllSystemsNominal()
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set: -> @ensureUserIsSpy()
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station = new SpyStation
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station.online = true # ensures user is a spy, then assigns true
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station.online # ensures all systems are nominal, then returns true
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```
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