ok
Mini Shell
'use strict'
const genfun = require('genfun')
class Duck extends Function {
// Duck.impl(Foo, [String, Array], { frob (str, arr) { ... }})
impl (target, types, impls) {
if (!impls && !isArray(types)) {
impls = types
types = []
}
if (!impls && this.isDerivable) {
impls = this._defaultImpls
}
if (!impls) {
impls = {}
}
if (typeof target === 'function' && !target.isGenfun) {
target = target.prototype
}
checkImpls(this, target, impls)
checkArgTypes(this, types)
this._constraints.forEach(c => {
if (!c.verify(target, types)) {
throw new Error(`Implementations of ${
this.name || 'this protocol'
} must first implement ${
c.parent.name || 'its constraint protocols defined in opts.where.'
}`)
}
})
this._methodNames.forEach(name => {
defineMethod(this, name, target, types, impls)
})
}
hasImpl (arg, args) {
args = args || []
const fns = this._methodNames
var gf
if (typeof arg === 'function' && !arg.isGenfun) {
arg = arg.prototype
}
args = args.map(arg => {
if (typeof arg === 'function' && !arg.isGenfun) {
return arg.prototype
} else {
return arg
}
})
for (var i = 0; i < fns.length; i++) {
gf = arg[fns[i]]
if (!gf ||
(gf.hasMethod
? !gf.hasMethod.apply(gf, args)
: typeof gf === 'function')) {
return false
}
}
return true
}
// MyDuck.matches('a', ['this', 'c'])
matches (thisType, argTypes) {
if (!argTypes && isArray(thisType)) {
argTypes = thisType
thisType = 'this'
}
if (!thisType) {
thisType = 'this'
}
if (!argTypes) {
argTypes = []
}
return new Constraint(this, thisType, argTypes)
}
}
Duck.prototype.isDuck = true
Duck.prototype.isProtocol = true
const Protoduck = module.exports = define(['duck'], {
createGenfun: ['duck', _metaCreateGenfun],
addMethod: ['duck', _metaAddMethod]
}, { name: 'Protoduck' })
const noImplFound = module.exports.noImplFound = genfun.noApplicableMethod
module.exports.define = define
function define (types, spec, opts) {
if (!isArray(types)) {
// protocol(spec, opts?) syntax for method-based protocols
opts = spec
spec = types
types = []
}
const duck = function (thisType, argTypes) {
return duck.matches(thisType, argTypes)
}
Object.setPrototypeOf(duck, Duck.prototype)
duck.isDerivable = true
Object.defineProperty(duck, 'name', {
value: (opts && opts.name) || 'Protocol'
})
if (opts && opts.where) {
let where = opts.where
if (!isArray(opts.where)) { where = [opts.where] }
duck._constraints = where.map(w => w.isProtocol // `where: [Foo]`
? w.matches()
: w
)
} else {
duck._constraints = []
}
duck.isProtocol = true
duck._metaobject = opts && opts.metaobject
duck._types = types
duck._defaultImpls = {}
duck._gfTypes = {}
duck._methodNames = Object.keys(spec)
duck._methodNames.forEach(name => {
checkMethodSpec(duck, name, spec)
})
duck._constraints.forEach(c => c.attach(duck))
return duck
}
function checkMethodSpec (duck, name, spec) {
let gfTypes = spec[name]
if (typeof gfTypes === 'function') {
duck._defaultImpls[name] = gfTypes
gfTypes = [gfTypes]
} if (typeof gfTypes[gfTypes.length - 1] === 'function') {
duck._defaultImpls[name] = gfTypes.pop()
} else {
duck.isDerivable = false
}
duck._gfTypes[name] = gfTypes.map(typeId => {
const idx = duck._types.indexOf(typeId)
if (idx === -1) {
throw new Error(
`type '${
typeId
}' for function '${
name
}' does not match any protocol types (${
duck._types.join(', ')
}).`
)
} else {
return idx
}
})
}
function defineMethod (duck, name, target, types, impls) {
const methodTypes = duck._gfTypes[name].map(function (typeIdx) {
return types[typeIdx]
})
for (let i = methodTypes.length - 1; i >= 0; i--) {
if (methodTypes[i] === undefined) {
methodTypes.pop()
} else {
break
}
}
const useMetaobject = duck._metaobject && duck._metaobject !== Protoduck
// `target` does not necessarily inherit from `Object`
if (!Object.prototype.hasOwnProperty.call(target, name)) {
// Make a genfun if there's nothing there
const gf = useMetaobject
? duck._metaobject.createGenfun(duck, target, name, null)
: _metaCreateGenfun(duck, target, name, null)
target[name] = gf
} else if (typeof target[name] === 'function' && !target[name].isGenfun) {
// Turn non-gf functions into genfuns
const gf = useMetaobject
? duck._metaobject.createGenfun(duck, target, name, target[name])
: _metaCreateGenfun(duck, target, name, target[name])
target[name] = gf
}
const fn = impls[name] || duck._defaultImpls[name]
if (fn) { // checkImpls made sure this is safe
useMetaobject
? duck._metaobject.addMethod(duck, target, name, methodTypes, fn)
: _metaAddMethod(duck, target, name, methodTypes, fn)
}
}
function checkImpls (duck, target, impls) {
duck._methodNames.forEach(function (name) {
if (
!impls[name] &&
!duck._defaultImpls[name] &&
// Existing methods on the target are acceptable defaults.
typeof target[name] !== 'function'
) {
throw new Error(`Missing implementation for ${
formatMethod(duck, name, duck.name)
}. Make sure the method is present in your ${
duck.name || 'protocol'
} definition. Required methods: ${
duck._methodNames.filter(m => {
return !duck._defaultImpls[m]
}).map(m => formatMethod(duck, m)).join(', ')
}.`)
}
})
Object.keys(impls).forEach(function (name) {
if (duck._methodNames.indexOf(name) === -1) {
throw new Error(
`${name}() was included in the impl, but is not part of ${
duck.name || 'the protocol'
}. Allowed methods: ${
duck._methodNames.map(m => formatMethod(duck, m)).join(', ')
}.`
)
}
})
}
function formatMethod (duck, name, withDuckName) {
return `${
withDuckName && duck.name ? `${duck.name}#` : ''
}${name}(${duck._gfTypes[name].map(n => duck._types[n]).join(', ')})`
}
function checkArgTypes (duck, types) {
var requiredTypes = duck._types
if (types.length > requiredTypes.length) {
throw new Error(
`${
duck.name || 'Protocol'
} expects to be defined across ${
requiredTypes.length
} type${requiredTypes.length > 1 ? 's' : ''}, but ${
types.length
} ${types.length > 1 ? 'were' : 'was'} specified.`
)
}
}
function typeName (obj) {
return (/\[object ([a-zA-Z0-9]+)\]/).exec(({}).toString.call(obj))[1]
}
function installMethodErrorMessage (proto, gf, target, name) {
noImplFound.add([gf], function (gf, thisArg, args) {
let parent = Object.getPrototypeOf(thisArg)
while (parent && parent[name] === gf) {
parent = Object.getPrototypeOf(parent)
}
if (parent && parent[name] && typeof parent[name] === 'function') {
}
var msg = `No ${typeName(thisArg)} impl for ${
proto.name ? `${proto.name}#` : ''
}${name}(${[].map.call(args, typeName).join(', ')}). You must implement ${
proto.name
? formatMethod(proto, name, true)
: `the protocol ${formatMethod(proto, name)} belongs to`
} in order to call ${typeName(thisArg)}#${name}(${
[].map.call(args, typeName).join(', ')
}).`
const err = new Error(msg)
err.protocol = proto
err.function = gf
err.thisArg = thisArg
err.args = args
err.code = 'ENOIMPL'
throw err
})
}
function isArray (x) {
return Object.prototype.toString.call(x) === '[object Array]'
}
// Metaobject Protocol
Protoduck.impl(Protoduck) // defaults configured by definition
function _metaCreateGenfun (proto, target, name, deflt) {
var gf = genfun({
default: deflt,
name: `${proto.name ? `${proto.name}#` : ''}${name}`
})
installMethodErrorMessage(proto, gf, target, name)
gf.duck = proto
return gf
}
function _metaAddMethod (duck, target, name, methodTypes, fn) {
return target[name].add(methodTypes, fn)
}
// Constraints
class Constraint {
constructor (parent, thisType, argTypes) {
this.parent = parent
this.target = thisType
this.types = argTypes
}
attach (obj) {
this.child = obj
if (this.target === 'this') {
this.thisIdx = 'this'
} else {
const idx = this.child._types.indexOf(this.target)
if (idx === -1) {
this.thisIdx = null
} else {
this.thisIdx = idx
}
}
this.indices = this.types.map(typeId => {
if (typeId === 'this') {
return 'this'
} else {
const idx = this.child._types.indexOf(typeId)
if (idx === -1) {
return null
} else {
return idx
}
}
})
}
verify (target, types) {
const thisType = (
this.thisIdx === 'this' || this.thisIdx == null
)
? target
: types[this.thisIdx]
const parentTypes = this.indices.map(idx => {
if (idx === 'this') {
return target
} else if (idx === 'this') {
return types[this.thisIdx]
} else if (idx === null) {
return Object
} else {
return types[idx] || Object.prototype
}
})
return this.parent.hasImpl(thisType, parentTypes)
}
}
Constraint.prototype.isConstraint = true
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