var abc = function(a, b, c) {
  return [a, b, c];
};
 
var curried = _.curry(abc);
 
curried(1)(2)(3);
// => [1, 2, 3]
 
curried(1, 2)(3);
// => [1, 2, 3]
 
curried(1, 2, 3);
// => [1, 2, 3]
 
// Curried with placeholders.
curried(1)(_, 3)(2);
// => [1, 2, 3]

/**
 * lodash (Custom Build) <https://lodash.com/>
 * Build: `lodash modularize exports="npm" -o ./`
 * Copyright jQuery Foundation and other contributors <https://jquery.org/>
 * Released under MIT license <https://lodash.com/license>
 * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
 * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 */

/** Used as the `TypeError` message for "Functions" methods. */
var FUNC_ERROR_TEXT = 'Expected a function';

/** Used as the internal argument placeholder. */
var PLACEHOLDER = '__lodash_placeholder__';

/** Used to compose bitmasks for function metadata. */
var BIND_FLAG = 1,
    BIND_KEY_FLAG = 2,
    CURRY_BOUND_FLAG = 4,
    CURRY_FLAG = 8,
    CURRY_RIGHT_FLAG = 16,
    PARTIAL_FLAG = 32,
    PARTIAL_RIGHT_FLAG = 64,
    ARY_FLAG = 128,
    REARG_FLAG = 256,
    FLIP_FLAG = 512;

/** Used as references for various `Number` constants. */
var INFINITY = 1 / 0,
    MAX_SAFE_INTEGER = 9007199254740991,
    MAX_INTEGER = 1.7976931348623157e+308,
    NAN = 0 / 0;

/** Used to associate wrap methods with their bit flags. */
var wrapFlags = [
  ['ary', ARY_FLAG],
  ['bind', BIND_FLAG],
  ['bindKey', BIND_KEY_FLAG],
  ['curry', CURRY_FLAG],
  ['curryRight', CURRY_RIGHT_FLAG],
  ['flip', FLIP_FLAG],
  ['partial', PARTIAL_FLAG],
  ['partialRight', PARTIAL_RIGHT_FLAG],
  ['rearg', REARG_FLAG]
];

/** `Object#toString` result references. */
var funcTag = '[object Function]',
    genTag = '[object GeneratorFunction]',
    symbolTag = '[object Symbol]';

/**
 * Used to match `RegExp`
 * [syntax characters](http://ecma-international.org/ecma-262/7.0/#sec-patterns).
 */
var reRegExpChar = /[\\^$.*+?()[\]{}|]/g;

/** Used to match leading and trailing whitespace. */
var reTrim = /^\s+|\s+$/g;

/** Used to match wrap detail comments. */
var reWrapComment = /\{(?:\n\/\* \[wrapped with .+\] \*\/)?\n?/,
    reWrapDetails = /\{\n\/\* \[wrapped with (.+)\] \*/,
    reSplitDetails = /,? & /;

/** Used to detect bad signed hexadecimal string values. */
var reIsBadHex = /^[-+]0x[0-9a-f]+$/i;

/** Used to detect binary string values. */
var reIsBinary = /^0b[01]+$/i;

/** Used to detect host constructors (Safari). */
var reIsHostCtor = /^\[object .+?Constructor\]$/;

/** Used to detect octal string values. */
var reIsOctal = /^0o[0-7]+$/i;

/** Used to detect unsigned integer values. */
var reIsUint = /^(?:0|[1-9]\d*)$/;

/** Built-in method references without a dependency on `root`. */
var freeParseInt = parseInt;

/** Detect free variable `global` from Node.js. */
var freeGlobal = typeof global == 'object' && global && global.Object === Object && global;

/** Detect free variable `self`. */
var freeSelf = typeof self == 'object' && self && self.Object === Object && self;

/** Used as a reference to the global object. */
var root = freeGlobal || freeSelf || Function('return this')();

/**
 * A faster alternative to `Function#apply`, this function invokes `func`
 * with the `this` binding of `thisArg` and the arguments of `args`.
 *
 * @private
 * @param {Function} func The function to invoke.
 * @param {*} thisArg The `this` binding of `func`.
 * @param {Array} args The arguments to invoke `func` with.
 * @returns {*} Returns the result of `func`.
 */
//一个速度更快的apply调用
function apply(func, thisArg, args) {
  switch (args.length) {
    case 0: return func.call(thisArg);
    case 1: return func.call(thisArg, args[0]);
    case 2: return func.call(thisArg, args[0], args[1]);
    case 3: return func.call(thisArg, args[0], args[1], args[2]);
  }
  return func.apply(thisArg, args);
}

/**
 * A specialized version of `_.forEach` for arrays without support for
 * iteratee shorthands.
 *
 * @private
 * @param {Array} [array] The array to iterate over.
 * @param {Function} iteratee The function invoked per iteration.
 * @returns {Array} Returns `array`.
 */
function arrayEach(array, iteratee) {
  var index = -1,
      length = array ? array.length : 0;

  while (++index < length) {
    if (iteratee(array[index], index, array) === false) {
      break;
    }
  }
  return array;
}

/**
 * A specialized version of `_.includes` for arrays without support for
 * specifying an index to search from.
 *
 * @private
 * @param {Array} [array] The array to inspect.
 * @param {*} target The value to search for.
 * @returns {boolean} Returns `true` if `target` is found, else `false`.
 */
function arrayIncludes(array, value) {
  var length = array ? array.length : 0;
  return !!length && baseIndexOf(array, value, 0) > -1;
}

/**
 * The base implementation of `_.findIndex` and `_.findLastIndex` without
 * support for iteratee shorthands.
 *
 * @private
 * @param {Array} array The array to inspect.
 * @param {Function} predicate The function invoked per iteration.
 * @param {number} fromIndex The index to search from.
 * @param {boolean} [fromRight] Specify iterating from right to left.
 * @returns {number} Returns the index of the matched value, else `-1`.
 */
function baseFindIndex(array, predicate, fromIndex, fromRight) {
  var length = array.length,
      index = fromIndex + (fromRight ? 1 : -1);

  while ((fromRight ? index-- : ++index < length)) {
    if (predicate(array[index], index, array)) {
      return index;
    }
  }
  return -1;
}

/**
 * The base implementation of `_.indexOf` without `fromIndex` bounds checks.
 *
 * @private
 * @param {Array} array The array to inspect.
 * @param {*} value The value to search for.
 * @param {number} fromIndex The index to search from.
 * @returns {number} Returns the index of the matched value, else `-1`.
 */
function baseIndexOf(array, value, fromIndex) {
  if (value !== value) {
    return baseFindIndex(array, baseIsNaN, fromIndex);
  }
  var index = fromIndex - 1,
      length = array.length;

  while (++index < length) {
    if (array[index] === value) {
      return index;
    }
  }
  return -1;
}

/**
 * The base implementation of `_.isNaN` without support for number objects.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is `NaN`, else `false`.
 */
function baseIsNaN(value) {
  return value !== value;
}

/**
 * Gets the number of `placeholder` occurrences in `array`.
 *
 * @private
 * @param {Array} array The array to inspect.
 * @param {*} placeholder The placeholder to search for.
 * @returns {number} Returns the placeholder count.
 */
//计算placeholder在array中出现次数
function countHolders(array, placeholder) {
  var length = array.length,//array长度
      result = 0;//结果，占位符出现次数

  while (length--) {//循环array，如果当前元素和placeholder相等，result自增1
    if (array[length] === placeholder) {
      result++;
    }
  }
  return result;
}

/**
 * Gets the value at `key` of `object`.
 *
 * @private
 * @param {Object} [object] The object to query.
 * @param {string} key The key of the property to get.
 * @returns {*} Returns the property value.
 */
function getValue(object, key) {
  return object == null ? undefined : object[key];
}

/**
 * Checks if `value` is a host object in IE < 9.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a host object, else `false`.
 */
function isHostObject(value) {
  // Many host objects are `Object` objects that can coerce to strings
  // despite having improperly defined `toString` methods.
  var result = false;
  if (value != null && typeof value.toString != 'function') {
    try {
      result = !!(value + '');
    } catch (e) {}
  }
  return result;
}

/**
 * Replaces all `placeholder` elements in `array` with an internal placeholder
 * and returns an array of their indexes.
 *
 * @private
 * @param {Array} array The array to modify.
 * @param {*} placeholder The placeholder to replace.
 * @returns {Array} Returns the new array of placeholder indexes.
 */
//替换数组中所有占位符元素为内部占位符然后返回一个它们的索引的数组
function replaceHolders(array, placeholder) {
  var index = -1,//循环索引
      length = array.length,//数组长度
      resIndex = 0,
      result = [];//结果数组

  while (++index < length) {
    var value = array[index];//数组的当前值
    if (value === placeholder || value === PLACEHOLDER) {//如果当前值是占位符
      array[index] = PLACEHOLDER;//就替换成内部占位符
      result[resIndex++] = index;//结果数组是数组中占位符的索引
    }
  }
  return result;
}

/** Used for built-in method references. */
var funcProto = Function.prototype,
    objectProto = Object.prototype;

/** Used to detect overreaching core-js shims. */
var coreJsData = root['__core-js_shared__'];

/** Used to detect methods masquerading as native. */
var maskSrcKey = (function() {
  var uid = /[^.]+$/.exec(coreJsData && coreJsData.keys && coreJsData.keys.IE_PROTO || '');
  return uid ? ('Symbol(src)_1.' + uid) : '';
}());

/** Used to resolve the decompiled source of functions. */
var funcToString = funcProto.toString;

/** Used to check objects for own properties. */
var hasOwnProperty = objectProto.hasOwnProperty;

/**
 * Used to resolve the
 * [`toStringTag`](http://ecma-international.org/ecma-262/7.0/#sec-object.prototype.tostring)
 * of values.
 */
var objectToString = objectProto.toString;

/** Used to detect if a method is native. */
var reIsNative = RegExp('^' +
  funcToString.call(hasOwnProperty).replace(reRegExpChar, '\\$&')
  .replace(/hasOwnProperty|(function).*?(?=\\\()| for .+?(?=\\\])/g, '$1.*?') + '$'
);

/** Built-in value references. */
var objectCreate = Object.create;

/* Built-in method references for those with the same name as other `lodash` methods. */
var nativeMax = Math.max,
    nativeMin = Math.min;

/* Used to set `toString` methods. */
var defineProperty = (function() {
  var func = getNative(Object, 'defineProperty'),
      name = getNative.name;

  return (name && name.length > 2) ? func : undefined;
}());

/**
 * The base implementation of `_.create` without support for assigning
 * properties to the created object.
 *
 * @private
 * @param {Object} prototype The object to inherit from.
 * @returns {Object} Returns the new object.
 */
//_.create的基础实现，创建继承自proto的新对象，不支持向被创建出来的新对象上指派新属性
function baseCreate(proto) {
  return isObject(proto) ? objectCreate(proto) : {};
  //判断proto是否是对象，调用Object.create处理
}

/**
 * The base implementation of `_.isNative` without bad shim checks.
 *
 * @private
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a native function,
 *  else `false`.
 */
function baseIsNative(value) {
  if (!isObject(value) || isMasked(value)) {
    return false;
  }
  var pattern = (isFunction(value) || isHostObject(value)) ? reIsNative : reIsHostCtor;
  return pattern.test(toSource(value));
}

/**
 * Creates an array that is the composition of partially applied arguments,
 * placeholders, and provided arguments into a single array of arguments.
 *
 * @private
 * @param {Array} args The provided arguments.
 * @param {Array} partials The arguments to prepend to those provided.
 * @param {Array} holders The `partials` placeholder indexes.
 * @params {boolean} [isCurried] Specify composing for a curried function.
 * @returns {Array} Returns the new array of composed arguments.
 */
//将局部应用参数，占位符和其他被提供的参数处理成最终结果参数数组返回
function composeArgs(args, partials, holders, isCurried) {
  var argsIndex = -1,//包裹方法接收到的参数数组循环索引
      argsLength = args.length,//包裹方法接收到的参数长度
      holdersLength = holders.length,//占位符索引数组的长度
      leftIndex = -1,//partials循环索引
      leftLength = partials.length,//partials长度
      rangeLength = nativeMax(argsLength - holdersLength, 0),
      //包裹方法接收到的参数长度减去占位符长度，需要填充占位符的包裹方法接收到的参数去除后剩余的参数长度
      result = Array(leftLength + rangeLength),//结果数组初始化
      isUncurried = !isCurried;//是否不是柯里化 标记

  while (++leftIndex < leftLength) {//先将局部应用参数插入结果数组
    result[leftIndex] = partials[leftIndex];
  }
  while (++argsIndex < holdersLength) {
    if (isUncurried || argsIndex < argsLength) {
      result[holders[argsIndex]] = args[argsIndex];
      //将占位符处的参数替换成包裹方法接收到的参数的开头对应的参数
    }
  }
  while (rangeLength--) {
     //需要填充占位符的包裹方法接收到的参数去除后剩余的参数插入结果数组最后
    result[leftIndex++] = args[argsIndex++];
  }
  return result;
}

/**
 * This function is like `composeArgs` except that the arguments composition
 * is tailored for `_.partialRight`.
 *
 * @private
 * @param {Array} args The provided arguments.
 * @param {Array} partials The arguments to append to those provided.
 * @param {Array} holders The `partials` placeholder indexes.
 * @params {boolean} [isCurried] Specify composing for a curried function.
 * @returns {Array} Returns the new array of composed arguments.
 */
//将局部应用参数，占位符和其他被提供的参数处理成最终结果参数数组返回
//局部应用参数添加到数组的最右边也就是结尾处
function composeArgsRight(args, partials, holders, isCurried) {
  var argsIndex = -1,//包裹方法接收到的参数数组循环索引
      argsLength = args.length,//包裹方法接收到的参数长度
      holdersIndex = -1,//占位符索引数组循环索引
      holdersLength = holders.length,//占位符索引数组的长度
      rightIndex = -1,//partials循环索引
      rightLength = partials.length,//partials长度
      rangeLength = nativeMax(argsLength - holdersLength, 0),
      //包裹方法接收到的参数长度减去占位符长度，需要填充占位符的包裹方法接收到的参数去除后剩余的参数长度
      result = Array(rangeLength + rightLength),//结果数组初始化
      isUncurried = !isCurried;//是否不是柯里化 标记

  //占位符填充参数和局部应用参数都往后放，先将最后剩余的参数存入结果数组
  while (++argsIndex < rangeLength) {
    result[argsIndex] = args[argsIndex];
  }
  var offset = argsIndex;//最后剩余的参数存入结果数组后的 参数数组偏移量
  while (++rightIndex < rightLength) {//将局部应用参数加入结果数组
    result[offset + rightIndex] = partials[rightIndex];
  }
  while (++holdersIndex < holdersLength) {//最后将占位符处的元素替换掉
    if (isUncurried || argsIndex < argsLength) {
      result[offset + holders[holdersIndex]] = args[argsIndex++];
    }
  }
  return result;
}

/**
 * Copies the values of `source` to `array`.
 *
 * @private
 * @param {Array} source The array to copy values from.
 * @param {Array} [array=[]] The array to copy values to.
 * @returns {Array} Returns `array`.
 */
function copyArray(source, array) {
  var index = -1,
      length = source.length;

  array || (array = Array(length));
  while (++index < length) {
    array[index] = source[index];
  }
  return array;
}

/**
 * Creates a function that wraps `func` to invoke it with the optional `this`
 * binding of `thisArg`.
 *
 * @private
 * @param {Function} func The function to wrap.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @param {*} [thisArg] The `this` binding of `func`.
 * @returns {Function} Returns the new wrapped function.
 */
function createBind(func, bitmask, thisArg) {
  var isBind = bitmask & BIND_FLAG,
      Ctor = createCtor(func);

  function wrapper() {
    var fn = (this && this !== root && this instanceof wrapper) ? Ctor : func;
    return fn.apply(isBind ? thisArg : this, arguments);
  }
  return wrapper;
}

/**
 * Creates a function that produces an instance of `Ctor` regardless of
 * whether it was invoked as part of a `new` expression or by `call` or `apply`.
 *
 * @private
 * @param {Function} Ctor The constructor to wrap.
 * @returns {Function} Returns the new wrapped function.
 */
//创建一个函数，它能够生成Ctor的新实例不管它是否被new调用或者call和apply调用
function createCtor(Ctor) {
  return function() {
    // Use a `switch` statement to work with class constructors. See
    // http://ecma-international.org/ecma-262/7.0/#sec-ecmascript-function-objects-call-thisargument-argumentslist
    // for more details.
    var args = arguments;
    switch (args.length) {//0~7的参数个数的时候直接返回new Ctor
      case 0: return new Ctor;
      case 1: return new Ctor(args[0]);
      case 2: return new Ctor(args[0], args[1]);
      case 3: return new Ctor(args[0], args[1], args[2]);
      case 4: return new Ctor(args[0], args[1], args[2], args[3]);
      case 5: return new Ctor(args[0], args[1], args[2], args[3], args[4]);
      case 6: return new Ctor(args[0], args[1], args[2], args[3], args[4], args[5]);
      case 7: return new Ctor(args[0], args[1], args[2], args[3], args[4], args[5], args[6]);
    }
    var thisBinding = baseCreate(Ctor.prototype),
    //this对象，是继承自Ctor.prototype的新对象，baseCreate调用原生的Object.create()
        result = Ctor.apply(thisBinding, args);//apply调用Ctor

    // Mimic the constructor's `return` behavior.
    // See https://es5.github.io/#x13.2.2 for more details.
    //模仿构造函数的return行为
    return isObject(result) ? result : thisBinding;
  };
}

/**
 * Creates a function that wraps `func` to enable currying.
 *
 * @private
 * @param {Function} func The function to wrap.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @param {number} arity The arity of `func`.
 * @returns {Function} Returns the new wrapped function.
 */
//创建一个包裹func函数的函数以启用柯里化
function createCurry(func, bitmask, arity) {
  var Ctor = createCtor(func);//基于func函数创建一个只能构造调用的func，也就是new调用

  function wrapper() {
    var length = arguments.length,//wrapper函数的参数列表长度
        args = Array(length),//args数组用于存储参数列表
        index = length,//循环索引，从结尾开始
        placeholder = getHolder(wrapper);//获取wrapper函数的占位符

    while (index--) {//循环参数列表长度
      args[index] = arguments[index];//将参数赋值到args数组中
    }
    var holders = (length < 3 && args[0] !== placeholder && args[length - 1] !== placeholder)
      ? []
      : replaceHolders(args, placeholder);
      //holders获取占位符在参数列表中的索引组成的数组
      //如果参数列表长度小于3，也就是最多两个参数，且两个参数都不是占位符，那么占位符的索引数组是空数组
      //否则调用replaceHolders获取占位符在参数列表中的索引组成的数组

    length -= holders.length;//参数列表长度减掉占位符的长度，也就是实际真正参数的个数
    if (length < arity) {//如果实际参数长度小于期望形参长度
      //调用createRecurry生成柯里化函数返回，createRecurry生成的函数可以继续接收下一个参数，直到所有参数接收完毕
      //注意arity参数减去了length，这样下一个柯里化函数的arity期望形参就会减少
      return createRecurry(
        func, bitmask, createHybrid, wrapper.placeholder, undefined,
        args, holders, undefined, undefined, arity - length);
    }
    var fn = (this && this !== root && this instanceof wrapper) ? Ctor : func;
    //如果是new调用，就使用Ctor作为func
    return apply(fn, this, args);
    //如果已经收集到了所有柯里化期望长度的参数，就将参数传递给fn获得最终结果
  }
  return wrapper;
}

/**
 * Creates a function that wraps `func` to invoke it with optional `this`
 * binding of `thisArg`, partial application, and currying.
 *
 * @private
 * @param {Function|string} func The function or method name to wrap.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @param {*} [thisArg] The `this` binding of `func`.
 * @param {Array} [partials] The arguments to prepend to those provided to
 *  the new function.
 * @param {Array} [holders] The `partials` placeholder indexes.
 * @param {Array} [partialsRight] The arguments to append to those provided
 *  to the new function.
 * @param {Array} [holdersRight] The `partialsRight` placeholder indexes.
 * @param {Array} [argPos] The argument positions of the new function.
 * @param {number} [ary] The arity cap of `func`.
 * @param {number} [arity] The arity of `func`.
 * @returns {Function} Returns the new wrapped function.
 */
//创建一个方法将func方法包裹，实现this绑定，或者局部应用或者柯里化
function createHybrid(func, bitmask, thisArg, partials, holders, partialsRight, holdersRight, argPos, ary, arity) {
  var isAry = bitmask & ARY_FLAG,//_.ary
      isBind = bitmask & BIND_FLAG,//_.bind
      isBindKey = bitmask & BIND_KEY_FLAG,//_.bindKey
      isCurried = bitmask & (CURRY_FLAG | CURRY_RIGHT_FLAG),//_.curry或_.curryRight
      isFlip = bitmask & FLIP_FLAG,//_.flip
      Ctor = isBindKey ? undefined : createCtor(func);
      //如果是_.bindKey调用，Ctor就赋值为undefined，否则创建一个只会返回new调用的func结果的构造函数

  function wrapper() {
    var length = arguments.length,//接收到的参数的长度
        args = Array(length),//args数组用于存储参数列表
        index = length;//循环索引

    while (index--) {//循环参数列表长度，将参数赋值到args数组中
      args[index] = arguments[index];
    }
    if (isCurried) {//如果是_.curry或_.curryRight调用
      var placeholder = getHolder(wrapper),//获取wrapper函数的占位符
          holdersCount = countHolders(args, placeholder);//占位符在args参数数组中出现次数
    }
    if (partials) {//如果有局部应用参数，调用composeArgs处理占位符，局部应用参数
      args = composeArgs(args, partials, holders, isCurried);
    }
    if (partialsRight) {//如果局部应用参数需要插入右边，调用composeArgsRight处理
      args = composeArgsRight(args, partialsRight, holdersRight, isCurried);
    }
    length -= holdersCount;//参数长度等于原长度减掉占位符的长度
    if (isCurried && length < arity) {//_.curry调用并且参数长度 小于 期望形参个数
      var newHolders = replaceHolders(args, placeholder);//获取参数中的占位符索引组成的数组
      //arity等于减去本次传入的参数个数，继续下一轮柯里化
      return createRecurry(
        func, bitmask, createHybrid, wrapper.placeholder, thisArg,
        args, newHolders, argPos, ary, arity - length
      );
    }
    var thisBinding = isBind ? thisArg : this,
        fn = isBindKey ? thisBinding[func] : func;//处理_.bind和_.bindKey的this

    length = args.length;//接收到的参数长度
    if (argPos) {
      args = reorder(args, argPos);
    } else if (isFlip && length > 1) {
      args.reverse();
    }
    if (isAry && ary < length) {
      args.length = ary;
    }
    if (this && this !== root && this instanceof wrapper) {
      fn = Ctor || createCtor(fn);
    }
    return fn.apply(thisBinding, args);
    //如果已经收集到了所有柯里化期望长度的参数，就将参数传递给fn获得最终结果
    //返回fn apply调用结果
  }
  return wrapper;
}

/**
 * Creates a function that wraps `func` to invoke it with the `this` binding
 * of `thisArg` and `partials` prepended to the arguments it receives.
 *
 * @private
 * @param {Function} func The function to wrap.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @param {*} thisArg The `this` binding of `func`.
 * @param {Array} partials The arguments to prepend to those provided to
 *  the new function.
 * @returns {Function} Returns the new wrapped function.
 */
function createPartial(func, bitmask, thisArg, partials) {
  var isBind = bitmask & BIND_FLAG,
      Ctor = createCtor(func);

  function wrapper() {
    var argsIndex = -1,
        argsLength = arguments.length,
        leftIndex = -1,
        leftLength = partials.length,
        args = Array(leftLength + argsLength),
        fn = (this && this !== root && this instanceof wrapper) ? Ctor : func;

    while (++leftIndex < leftLength) {
      args[leftIndex] = partials[leftIndex];
    }
    while (argsLength--) {
      args[leftIndex++] = arguments[++argsIndex];
    }
    return apply(fn, isBind ? thisArg : this, args);
  }
  return wrapper;
}

/**
 * Creates a function that wraps `func` to continue currying.
 *
 * @private
 * @param {Function} func The function to wrap.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @param {Function} wrapFunc The function to create the `func` wrapper.
 * @param {*} placeholder The placeholder value.
 * @param {*} [thisArg] The `this` binding of `func`.
 * @param {Array} [partials] The arguments to prepend to those provided to
 *  the new function.
 * @param {Array} [holders] The `partials` placeholder indexes.
 * @param {Array} [argPos] The argument positions of the new function.
 * @param {number} [ary] The arity cap of `func`.
 * @param {number} [arity] The arity of `func`.
 * @returns {Function} Returns the new wrapped function.
 */
//创建一个函数包裹func继续进行柯里化操作
//func需要柯里化的函数，bitmask掩码标志，wrapFunc做包裹的函数createHybrid，placeholder占位符，thisArg需要绑定的this，partials局部应用参数组成的数组，holders占位符在参数数组中的索引组成的数组，argPos新函数的参数位置，ary期望参数个数上限，arity期望形参个数
function createRecurry(func, bitmask, wrapFunc, placeholder, thisArg, partials, holders, argPos, ary, arity) {
  var isCurry = bitmask & CURRY_FLAG,//是否是_.curry调用
      newHolders = isCurry ? holders : undefined,//占位符索引数组
      newHoldersRight = isCurry ? undefined : holders,//右边的占位符索引数组
      newPartials = isCurry ? partials : undefined,//局部应用参数数组
      newPartialsRight = isCurry ? undefined : partials;//局部应用到右边的参数数组

  bitmask |= (isCurry ? PARTIAL_FLAG : PARTIAL_RIGHT_FLAG);//为掩码加上局部应用对应二进制位数
  bitmask &= ~(isCurry ? PARTIAL_RIGHT_FLAG : PARTIAL_FLAG);//只保留除了局部应用位数以外的二进制位数

  if (!(bitmask & CURRY_BOUND_FLAG)) {//如果不是柯里化 有界函数
    bitmask &= ~(BIND_FLAG | BIND_KEY_FLAG);//保留除了绑定this位数出外的二进制位数
  }

  var result = wrapFunc(func, bitmask, thisArg, newPartials, newHolders, newPartialsRight, newHoldersRight, argPos, ary, arity);//调用createHybrid处理
  result.placeholder = placeholder;
  return setWrapToString(result, func, bitmask);
}

/**
 * Creates a function that either curries or invokes `func` with optional
 * `this` binding and partially applied arguments.
 *
 * @private
 * @param {Function|string} func The function or method name to wrap.
 * @param {number} bitmask The bitmask flags.
 *  The bitmask may be composed of the following flags:
 *     1 - `_.bind`
 *     2 - `_.bindKey`
 *     4 - `_.curry` or `_.curryRight` of a bound function
 *     8 - `_.curry`
 *    16 - `_.curryRight`
 *    32 - `_.partial`
 *    64 - `_.partialRight`
 *   128 - `_.rearg`
 *   256 - `_.ary`
 *   512 - `_.flip`
 * @param {*} [thisArg] The `this` binding of `func`.
 * @param {Array} [partials] The arguments to be partially applied.
 * @param {Array} [holders] The `partials` placeholder indexes.
 * @param {Array} [argPos] The argument positions of the new function.
 * @param {number} [ary] The arity cap of `func`.
 * @param {number} [arity] The arity of `func`.
 * @returns {Function} Returns the new wrapped function.
 */
//创建包裹好的函数，做柯里化或者绑定this或者处理局部应用参数
//ary是arity上限，arity是期望参数个数，也就是形参个数
function createWrap(func, bitmask, thisArg, partials, holders, argPos, ary, arity) {
  var isBindKey = bitmask & BIND_KEY_FLAG;
  if (!isBindKey && typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  var length = partials ? partials.length : 0;
  if (!length) {
    bitmask &= ~(PARTIAL_FLAG | PARTIAL_RIGHT_FLAG);
    partials = holders = undefined;
  }
  ary = ary === undefined ? ary : nativeMax(toInteger(ary), 0);
  arity = arity === undefined ? arity : toInteger(arity);//将arity转换成整数
  length -= holders ? holders.length : 0;

  if (bitmask & PARTIAL_RIGHT_FLAG) {
    var partialsRight = partials,
        holdersRight = holders;

    partials = holders = undefined;
  }

  var newData = [
    func, bitmask, thisArg, partials, holders, partialsRight, holdersRight,
    argPos, ary, arity
  ];

  func = newData[0];
  bitmask = newData[1];
  thisArg = newData[2];
  partials = newData[3];
  holders = newData[4];
  arity = newData[9] = newData[9] == null
    ? (isBindKey ? 0 : func.length)
    : nativeMax(newData[9] - length, 0);
    //如果原arity为空，那么判断是否是_.bindKey调用，如果是就赋值为0，如果不是就赋值为func的length属性，形参个数
    //如果原arity不为空，那么原arity减去0（此处是0，因为没有局部应用和占位符，否则要减去 局部应用长度减占位符 的结果）

  if (!arity && bitmask & (CURRY_FLAG | CURRY_RIGHT_FLAG)) {
    bitmask &= ~(CURRY_FLAG | CURRY_RIGHT_FLAG);
  }
  if (!bitmask || bitmask == BIND_FLAG) {
    var result = createBind(func, bitmask, thisArg);
  } else if (bitmask == CURRY_FLAG || bitmask == CURRY_RIGHT_FLAG) {
    //如果掩码代表调用_.curry或者_.curryRight，调用createCurry获取结果
    result = createCurry(func, bitmask, arity);
  } else if ((bitmask == PARTIAL_FLAG || bitmask == (BIND_FLAG | PARTIAL_FLAG)) && !holders.length) {
    result = createPartial(func, bitmask, thisArg, partials);
  } else {
    result = createHybrid.apply(undefined, newData);
  }
  return setWrapToString(result, func, bitmask);
}

/**
 * Gets the argument placeholder value for `func`.
 *
 * @private
 * @param {Function} func The function to inspect.
 * @returns {*} Returns the placeholder value.
 */
//获取func函数的占位符
function getHolder(func) {
  var object = func;
  return object.placeholder;
}

/**
 * Gets the native function at `key` of `object`.
 *
 * @private
 * @param {Object} object The object to query.
 * @param {string} key The key of the method to get.
 * @returns {*} Returns the function if it's native, else `undefined`.
 */
function getNative(object, key) {
  var value = getValue(object, key);
  return baseIsNative(value) ? value : undefined;
}

/**
 * Extracts wrapper details from the `source` body comment.
 *
 * @private
 * @param {string} source The source to inspect.
 * @returns {Array} Returns the wrapper details.
 */
function getWrapDetails(source) {
  var match = source.match(reWrapDetails);
  return match ? match[1].split(reSplitDetails) : [];
}

/**
 * Inserts wrapper `details` in a comment at the top of the `source` body.
 *
 * @private
 * @param {string} source The source to modify.
 * @returns {Array} details The details to insert.
 * @returns {string} Returns the modified source.
 */
function insertWrapDetails(source, details) {
  var length = details.length,
      lastIndex = length - 1;

  details[lastIndex] = (length > 1 ? '& ' : '') + details[lastIndex];
  details = details.join(length > 2 ? ', ' : ' ');
  return source.replace(reWrapComment, '{\n/* [wrapped with ' + details + '] */\n');
}

/**
 * Checks if `value` is a valid array-like index.
 *
 * @private
 * @param {*} value The value to check.
 * @param {number} [length=MAX_SAFE_INTEGER] The upper bounds of a valid index.
 * @returns {boolean} Returns `true` if `value` is a valid index, else `false`.
 */
function isIndex(value, length) {
  length = length == null ? MAX_SAFE_INTEGER : length;
  return !!length &&
    (typeof value == 'number' || reIsUint.test(value)) &&
    (value > -1 && value % 1 == 0 && value < length);
}

/**
 * Checks if `func` has its source masked.
 *
 * @private
 * @param {Function} func The function to check.
 * @returns {boolean} Returns `true` if `func` is masked, else `false`.
 */
function isMasked(func) {
  return !!maskSrcKey && (maskSrcKey in func);
}

/**
 * Reorder `array` according to the specified indexes where the element at
 * the first index is assigned as the first element, the element at
 * the second index is assigned as the second element, and so on.
 *
 * @private
 * @param {Array} array The array to reorder.
 * @param {Array} indexes The arranged array indexes.
 * @returns {Array} Returns `array`.
 */
function reorder(array, indexes) {
  var arrLength = array.length,
      length = nativeMin(indexes.length, arrLength),
      oldArray = copyArray(array);

  while (length--) {
    var index = indexes[length];
    array[length] = isIndex(index, arrLength) ? oldArray[index] : undefined;
  }
  return array;
}

/**
 * Sets the `toString` method of `wrapper` to mimic the source of `reference`
 * with wrapper details in a comment at the top of the source body.
 *
 * @private
 * @param {Function} wrapper The function to modify.
 * @param {Function} reference The reference function.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @returns {Function} Returns `wrapper`.
 */
var setWrapToString = !defineProperty ? identity : function(wrapper, reference, bitmask) {
  var source = (reference + '');
  return defineProperty(wrapper, 'toString', {
    'configurable': true,
    'enumerable': false,
    'value': constant(insertWrapDetails(source, updateWrapDetails(getWrapDetails(source), bitmask)))
  });
};

/**
 * Converts `func` to its source code.
 *
 * @private
 * @param {Function} func The function to process.
 * @returns {string} Returns the source code.
 */
function toSource(func) {
  if (func != null) {
    try {
      return funcToString.call(func);
    } catch (e) {}
    try {
      return (func + '');
    } catch (e) {}
  }
  return '';
}

/**
 * Updates wrapper `details` based on `bitmask` flags.
 *
 * @private
 * @returns {Array} details The details to modify.
 * @param {number} bitmask The bitmask flags. See `createWrap` for more details.
 * @returns {Array} Returns `details`.
 */
function updateWrapDetails(details, bitmask) {
  arrayEach(wrapFlags, function(pair) {
    var value = '_.' + pair[0];
    if ((bitmask & pair[1]) && !arrayIncludes(details, value)) {
      details.push(value);
    }
  });
  return details.sort();
}

/**
 * Creates a function that accepts arguments of `func` and either invokes
 * `func` returning its result, if at least `arity` number of arguments have
 * been provided, or returns a function that accepts the remaining `func`
 * arguments, and so on. The arity of `func` may be specified if `func.length`
 * is not sufficient.
 *
 * The `_.curry.placeholder` value, which defaults to `_` in monolithic builds,
 * may be used as a placeholder for provided arguments.
 *
 * **Note:** This method doesn't set the "length" property of curried functions.
 *
 * @static
 * @memberOf _
 * @since 2.0.0
 * @category Function
 * @param {Function} func The function to curry.
 * @param {number} [arity=func.length] The arity of `func`.
 * @param- {Object} [guard] Enables use as an iteratee for methods like `_.map`.
 * @returns {Function} Returns the new curried function.
 * @example
 *
 * var abc = function(a, b, c) {
 *   return [a, b, c];
 * };
 *
 * var curried = _.curry(abc);
 *
 * curried(1)(2)(3);
 * // => [1, 2, 3]
 *
 * curried(1, 2)(3);
 * // => [1, 2, 3]
 *
 * curried(1, 2, 3);
 * // => [1, 2, 3]
 *
 * // Curried with placeholders.
 * curried(1)(_, 3)(2);
 * // => [1, 2, 3]
 */
//创建一个方法接受func的参数列表，要么调用func返回其结果，在 至少arity参数数量被提供的情况下；要么返回一个函数继续接受剩余的func的参数。如果func.length不够充足，arity参数可能被指定
//默认用下划线作为参数占位符
function curry(func, arity, guard) {
  arity = guard ? undefined : arity;
  //如果func要作为一个iteratee使用，arity参数个数就为undefined
  var result = createWrap(func, CURRY_FLAG, undefined, undefined, undefined, undefined, undefined, arity);//调用createWrap处理
  result.placeholder = curry.placeholder;
  return result;
}

/**
 * Checks if `value` is classified as a `Function` object.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a function, else `false`.
 * @example
 *
 * _.isFunction(_);
 * // => true
 *
 * _.isFunction(/abc/);
 * // => false
 */
function isFunction(value) {
  // The use of `Object#toString` avoids issues with the `typeof` operator
  // in Safari 8-9 which returns 'object' for typed array and other constructors.
  var tag = isObject(value) ? objectToString.call(value) : '';
  return tag == funcTag || tag == genTag;
}

/**
 * Checks if `value` is the
 * [language type](http://www.ecma-international.org/ecma-262/7.0/#sec-ecmascript-language-types)
 * of `Object`. (e.g. arrays, functions, objects, regexes, `new Number(0)`, and `new String('')`)
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is an object, else `false`.
 * @example
 *
 * _.isObject({});
 * // => true
 *
 * _.isObject([1, 2, 3]);
 * // => true
 *
 * _.isObject(_.noop);
 * // => true
 *
 * _.isObject(null);
 * // => false
 */
function isObject(value) {
  var type = typeof value;
  return !!value && (type == 'object' || type == 'function');
}

/**
 * Checks if `value` is object-like. A value is object-like if it's not `null`
 * and has a `typeof` result of "object".
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is object-like, else `false`.
 * @example
 *
 * _.isObjectLike({});
 * // => true
 *
 * _.isObjectLike([1, 2, 3]);
 * // => true
 *
 * _.isObjectLike(_.noop);
 * // => false
 *
 * _.isObjectLike(null);
 * // => false
 */
function isObjectLike(value) {
  return !!value && typeof value == 'object';
}

/**
 * Checks if `value` is classified as a `Symbol` primitive or object.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to check.
 * @returns {boolean} Returns `true` if `value` is a symbol, else `false`.
 * @example
 *
 * _.isSymbol(Symbol.iterator);
 * // => true
 *
 * _.isSymbol('abc');
 * // => false
 */
function isSymbol(value) {
  return typeof value == 'symbol' ||
    (isObjectLike(value) && objectToString.call(value) == symbolTag);
}

/**
 * Converts `value` to a finite number.
 *
 * @static
 * @memberOf _
 * @since 4.12.0
 * @category Lang
 * @param {*} value The value to convert.
 * @returns {number} Returns the converted number.
 * @example
 *
 * _.toFinite(3.2);
 * // => 3.2
 *
 * _.toFinite(Number.MIN_VALUE);
 * // => 5e-324
 *
 * _.toFinite(Infinity);
 * // => 1.7976931348623157e+308
 *
 * _.toFinite('3.2');
 * // => 3.2
 */
function toFinite(value) {
  if (!value) {
    return value === 0 ? value : 0;
  }
  value = toNumber(value);
  if (value === INFINITY || value === -INFINITY) {
    var sign = (value < 0 ? -1 : 1);
    return sign * MAX_INTEGER;
  }
  return value === value ? value : 0;
}

/**
 * Converts `value` to an integer.
 *
 * **Note:** This method is loosely based on
 * [`ToInteger`](http://www.ecma-international.org/ecma-262/7.0/#sec-tointeger).
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to convert.
 * @returns {number} Returns the converted integer.
 * @example
 *
 * _.toInteger(3.2);
 * // => 3
 *
 * _.toInteger(Number.MIN_VALUE);
 * // => 0
 *
 * _.toInteger(Infinity);
 * // => 1.7976931348623157e+308
 *
 * _.toInteger('3.2');
 * // => 3
 */
function toInteger(value) {
  var result = toFinite(value),
      remainder = result % 1;

  return result === result ? (remainder ? result - remainder : result) : 0;
}

/**
 * Converts `value` to a number.
 *
 * @static
 * @memberOf _
 * @since 4.0.0
 * @category Lang
 * @param {*} value The value to process.
 * @returns {number} Returns the number.
 * @example
 *
 * _.toNumber(3.2);
 * // => 3.2
 *
 * _.toNumber(Number.MIN_VALUE);
 * // => 5e-324
 *
 * _.toNumber(Infinity);
 * // => Infinity
 *
 * _.toNumber('3.2');
 * // => 3.2
 */
function toNumber(value) {
  if (typeof value == 'number') {
    return value;
  }
  if (isSymbol(value)) {
    return NAN;
  }
  if (isObject(value)) {
    var other = typeof value.valueOf == 'function' ? value.valueOf() : value;
    value = isObject(other) ? (other + '') : other;
  }
  if (typeof value != 'string') {
    return value === 0 ? value : +value;
  }
  value = value.replace(reTrim, '');
  var isBinary = reIsBinary.test(value);
  return (isBinary || reIsOctal.test(value))
    ? freeParseInt(value.slice(2), isBinary ? 2 : 8)
    : (reIsBadHex.test(value) ? NAN : +value);
}

/**
 * Creates a function that returns `value`.
 *
 * @static
 * @memberOf _
 * @since 2.4.0
 * @category Util
 * @param {*} value The value to return from the new function.
 * @returns {Function} Returns the new constant function.
 * @example
 *
 * var objects = _.times(2, _.constant({ 'a': 1 }));
 *
 * console.log(objects);
 * // => [{ 'a': 1 }, { 'a': 1 }]
 *
 * console.log(objects[0] === objects[1]);
 * // => true
 */
function constant(value) {
  return function() {
    return value;
  };
}

/**
 * This method returns the first argument it receives.
 *
 * @static
 * @since 0.1.0
 * @memberOf _
 * @category Util
 * @param {*} value Any value.
 * @returns {*} Returns `value`.
 * @example
 *
 * var object = { 'a': 1 };
 *
 * console.log(_.identity(object) === object);
 * // => true
 */
function identity(value) {
  return value;
}

// Assign default placeholders.
curry.placeholder = {};

module.exports = curry;

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