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Filename :
genfun.js
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'use strict' const Method = require('./method') const Role = require('./role') const util = require('./util') const kCache = Symbol('cache') const kDefaultMethod = Symbol('defaultMethod') const kMethods = Symbol('methods') const kNoNext = Symbol('noNext') module.exports = function genfun (opts) { function gf () { if (!gf[kMethods].length && gf[kDefaultMethod]) { return gf[kDefaultMethod].func.apply(this, arguments) } else { return gf.applyGenfun(this, arguments) } } Object.setPrototypeOf(gf, Genfun.prototype) gf[kMethods] = [] gf[kCache] = {key: [], methods: [], state: STATES.UNINITIALIZED} if (opts && typeof opts === 'function') { gf.add(opts) } else if (opts && opts.default) { gf.add(opts.default) } if (opts && opts.name) { Object.defineProperty(gf, 'name', { value: opts.name }) } if (opts && opts.noNextMethod) { gf[kNoNext] = true } return gf } class Genfun extends Function {} Genfun.prototype.isGenfun = true const STATES = { UNINITIALIZED: 0, MONOMORPHIC: 1, POLYMORPHIC: 2, MEGAMORPHIC: 3 } const MAX_CACHE_SIZE = 32 /** * Defines a method on a generic function. * * @function * @param {Array-like} selector - Selector array for dispatching the method. * @param {Function} methodFunction - Function to execute when the method * successfully dispatches. */ Genfun.prototype.add = function addMethod (selector, func) { if (!func && typeof selector === 'function') { func = selector selector = [] } selector = [].slice.call(selector) for (var i = 0; i < selector.length; i++) { if (!selector.hasOwnProperty(i)) { selector[i] = Object.prototype } } this[kCache] = {key: [], methods: [], state: STATES.UNINITIALIZED} let method = new Method(this, selector, func) if (selector.length) { this[kMethods].push(method) } else { this[kDefaultMethod] = method } return this } /** * Removes a previously-defined method on `genfun` that matches * `selector` exactly. * * @function * @param {Genfun} genfun - Genfun to remove a method from. * @param {Array-like} selector - Objects to match on when finding a * method to remove. */ Genfun.prototype.rm = function removeMethod () { throw new Error('not yet implemented') } /** * Returns true if there are methods that apply to the given arguments on * `genfun`. Additionally, makes sure the cache is warmed up for the given * arguments. * */ Genfun.prototype.hasMethod = function hasMethod () { const methods = this.getApplicableMethods(arguments) return !!(methods && methods.length) } /** * This generic function is called when `genfun` has been called and no * applicable method was found. The default method throws an `Error`. * * @function * @param {Genfun} genfun - Generic function instance that was called. * @param {*} newthis - value of `this` the genfun was called with. * @param {Array} callArgs - Arguments the genfun was called with. */ module.exports.noApplicableMethod = module.exports() module.exports.noApplicableMethod.add([], (gf, thisArg, args) => { let msg = 'No applicable method found when called with arguments of types: (' + [].map.call(args, (arg) => { return (/\[object ([a-zA-Z0-9]+)\]/) .exec(({}).toString.call(arg))[1] }).join(', ') + ')' let err = new Error(msg) err.genfun = gf err.thisArg = thisArg err.args = args throw err }) /* * Internal */ Genfun.prototype.applyGenfun = function applyGenfun (newThis, args) { let applicableMethods = this.getApplicableMethods(args) if (applicableMethods.length === 1 || this[kNoNext]) { return applicableMethods[0].func.apply(newThis, args) } else if (applicableMethods.length > 1) { let idx = 0 const nextMethod = function nextMethod () { if (arguments.length) { // Replace args if passed in explicitly args = arguments Array.prototype.push.call(args, nextMethod) } const next = applicableMethods[idx++] if (idx >= applicableMethods.length) { Array.prototype.pop.call(args) } return next.func.apply(newThis, args) } Array.prototype.push.call(args, nextMethod) return nextMethod() } else { return module.exports.noApplicableMethod(this, newThis, args) } } Genfun.prototype.getApplicableMethods = function getApplicableMethods (args) { if (!args.length || !this[kMethods].length) { return this[kDefaultMethod] ? [this[kDefaultMethod]] : [] } let applicableMethods let maybeMethods = cachedMethods(this, args) if (maybeMethods) { applicableMethods = maybeMethods } else { applicableMethods = computeApplicableMethods(this, args) cacheArgs(this, args, applicableMethods) } return applicableMethods } function cacheArgs (genfun, args, methods) { if (genfun[kCache].state === STATES.MEGAMORPHIC) { return } var key = [] var proto for (var i = 0; i < args.length; i++) { proto = cacheableProto(genfun, args[i]) if (proto) { key[i] = proto } else { return null } } genfun[kCache].key.unshift(key) genfun[kCache].methods.unshift(methods) if (genfun[kCache].key.length === 1) { genfun[kCache].state = STATES.MONOMORPHIC } else if (genfun[kCache].key.length < MAX_CACHE_SIZE) { genfun[kCache].state = STATES.POLYMORPHIC } else { genfun[kCache].state = STATES.MEGAMORPHIC } } function cacheableProto (genfun, arg) { var dispatchable = util.dispatchableObject(arg) if (Object.hasOwnProperty.call(dispatchable, Role.roleKeyName)) { for (var j = 0; j < dispatchable[Role.roleKeyName].length; j++) { var role = dispatchable[Role.roleKeyName][j] if (role.method.genfun === genfun) { return null } } } return Object.getPrototypeOf(dispatchable) } function cachedMethods (genfun, args) { if (genfun[kCache].state === STATES.UNINITIALIZED || genfun[kCache].state === STATES.MEGAMORPHIC) { return null } var protos = [] var proto for (var i = 0; i < args.length; i++) { proto = cacheableProto(genfun, args[i]) if (proto) { protos[i] = proto } else { return } } for (i = 0; i < genfun[kCache].key.length; i++) { if (matchCachedMethods(genfun[kCache].key[i], protos)) { return genfun[kCache].methods[i] } } } function matchCachedMethods (key, protos) { if (key.length !== protos.length) { return false } for (var i = 0; i < key.length; i++) { if (key[i] !== protos[i]) { return false } } return true } function computeApplicableMethods (genfun, args) { args = [].slice.call(args) let discoveredMethods = [] function findAndRankRoles (object, hierarchyPosition, index) { var roles = Object.hasOwnProperty.call(object, Role.roleKeyName) ? object[Role.roleKeyName] : [] roles.forEach(role => { if (role.method.genfun === genfun && index === role.position) { if (discoveredMethods.indexOf(role.method) < 0) { Method.clearRank(role.method) discoveredMethods.push(role.method) } Method.setRankHierarchyPosition(role.method, index, hierarchyPosition) } }) // When a discovered method would receive more arguments than // were specialized, we pretend all extra arguments have a role // on Object.prototype. if (util.isObjectProto(object)) { discoveredMethods.forEach(method => { if (method.minimalSelector <= index) { Method.setRankHierarchyPosition(method, index, hierarchyPosition) } }) } } args.forEach((arg, index) => { getPrecedenceList(util.dispatchableObject(arg)) .forEach((obj, hierarchyPosition) => { findAndRankRoles(obj, hierarchyPosition, index) }) }) let applicableMethods = discoveredMethods.filter(method => { return (args.length === method._rank.length && Method.isFullySpecified(method)) }) applicableMethods.sort((a, b) => Method.score(a) - Method.score(b)) if (genfun[kDefaultMethod]) { applicableMethods.push(genfun[kDefaultMethod]) } return applicableMethods } /* * Helper function for getting an array representing the entire * inheritance/precedence chain for an object by navigating its * prototype pointers. */ function getPrecedenceList (obj) { var precedenceList = [] var nextObj = obj while (nextObj) { precedenceList.push(nextObj) nextObj = Object.getPrototypeOf(nextObj) } return precedenceList }