scontainers/dist/decorators/slice.js

A container/collection/iterator library for JavaScript, comfortable to use, performant and versatile.

"use strict";

function _implSymbol(target, sym, value) {
  Object.defineProperty(target, sym, {
    value,
    configurable: true
  });
  return target[sym];
}

function _getSymbol(targetSymName, ...traitSets) {
  let symbol;
  traitSets.forEach(traitSet => {
    const sym = traitSet[targetSymName];

    if (typeof sym === 'symbol') {
      if (!!symbol && symbol !== sym) {
        throw new Error(`Symbol ${targetSymName} offered by multiple trait sets.`);
      }

      symbol = sym;
    }
  });

  if (!symbol) {
    throw new Error(`No trait set is providing symbol ${targetSymName}.`);
  }

  return symbol;
}

function _testTraitSet(traitSet) {
  if (!traitSet || typeof traitSet === 'boolean' || typeof traitSet === 'number' || typeof traitSet === 'string') {
    throw new Error(`${traitSet} cannot be used as a trait set.`);
  }
}

const {
  assert,
  traits,
  id
} = require('../utils.js');

_testTraitSet(traits.utils);

_testTraitSet(traits.scontainers);

_testTraitSet(traits.semantics);

const _nth = _getSymbol("nth", traits.utils, traits.scontainers, traits.semantics);

const _len = _getSymbol("len", traits.utils, traits.scontainers, traits.semantics);

const _describeScontainer = _getSymbol("describeScontainer", traits.utils, traits.scontainers, traits.semantics);

const _implCoreGenerators = _getSymbol("implCoreGenerators", traits.utils, traits.scontainers, traits.semantics);

const _plus = _getSymbol("plus", traits.utils, traits.scontainers, traits.semantics);

const _minus = _getSymbol("minus", traits.utils, traits.scontainers, traits.semantics);

const _implCoreTraits = _getSymbol("implCoreTraits", traits.utils, traits.scontainers, traits.semantics);

module.exports = function (ParentCollection) {
  if (!ParentCollection.prototype[_nth]) {
    return;
  }

  return function () {
    class Slice {
      static get name() {
        return `${ParentCollection.name}::Slice`;
      }

      constructor(coll, begin, end = coll[_len]()) {
        this.wrapped = coll;
        this.begin = begin;
        this.end = end;
        assert(this.begin >= 0 && this.end <= coll[_len]() && this.end >= this.begin);
      }

      toString() {
        return `${this.wrapped}[${this.begin}:${this.end}]`;
      }

    }

    const parentProto = ParentCollection.prototype;

    Slice[_describeScontainer]({
      InnerCollection: ParentCollection,
      innerCollectionKey: id`wrapped`,
      argKeys: [id`begin`, id`end`]
    });

    Slice[_implCoreGenerators]({
      stage(kvn) {
        return kvn;
      },

      indexToParentIndex(index) {
        return index[_plus](this.args.begin);
      },

      len() {
        if (parentProto[_len]) {
          return function () {
            return this.args.end[_minus](this.args.begin);
          };
        }
      }

    });

    Slice[_implCoreTraits]({
      stage(kvn) {
        return kvn;
      },

      indexToParentIndex(index) {
        return index + this.begin;
      },

      len() {
        if (parentProto[_len]) {
          return function () {
            return this.end - this.begin;
          };
        }
      }

    });

    return Slice;
  };
};