git ssb

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var Value = require('./value')
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var LazyWatcher = require('./lib/lazy-watcher')
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var isSame = require('./lib/is-same')
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module.exports = Struct
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var blackList = {
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  'length': 'Clashes with `Function.prototype.length`.\n',
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  'name': 'Clashes with `Function.prototype.name`\n',
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  'destroy': '`destroy` is a reserved key of struct\n'
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}
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function Struct (properties, opts) {
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  var object = Object.create({})
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  var releases = []
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  var binder = LazyWatcher(update, listen, unlisten)
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  binder.value = object
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  var comparer = opts && opts.comparer || null
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  var observable = function MutantStruct (listener) {
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    if (!listener) {
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      return binder.getValue()
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    }
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    return binder.addListener(listener)
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  }
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  var keys = Object.keys(properties)
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  var suspendBroadcast = false
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  keys.forEach(function (key) {
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    if (blackList.hasOwnProperty(key)) {
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      throw new Error("Cannot create a struct with a key named '" + key + "'.\n" + blackList[key])
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    }
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    var obs = typeof properties[key] === 'function'
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      ? properties[key]
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      : Value(properties[key])
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    object[key] = obs()
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    observable[key] = obs
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  })
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  observable.set = function (values) {
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    var lastValue = suspendBroadcast
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    suspendBroadcast = true
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    values = values || {}
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    // update inner observables
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    keys.forEach(function (key) {
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      if (observable[key]() !== values[key]) {
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        observable[key].set(values[key])
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      }
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    })
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    // store additional keys (but don't create observables)
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    Object.keys(values).forEach(function (key) {
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      if (!(key in properties)) {
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        object[key] = values[key]
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      }
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    })
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    suspendBroadcast = lastValue
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    if (!suspendBroadcast) {
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      binder.broadcast()
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    }
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  }
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  return observable
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  // scoped
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  function listen () {
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    keys.map(function (key) {
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      var obs = observable[key]
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      releases.push(obs(function (val) {
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        if (!isSame(val, object[key], comparer)) {
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          object[key] = val
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          if (!suspendBroadcast) {
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            binder.broadcast(object)
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          }
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        }
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      }))
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    })
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  }
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  function unlisten () {
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    while (releases.length) {
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      releases.pop()()
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    }
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  }
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  function update () {
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    var changed = false
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    keys.forEach(function (key) {
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      var newValue = observable[key]()
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      if (!isSame(newValue, object[key], comparer)) {
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        object[key] = observable[key]()
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        changed = true
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      }
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    })
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    return changed
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  }
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}
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