RethinkDB-resembling type-aware value comparison (experiment)

rcompare.js

const _ = require("lodash");

function inferTypeOf(value) {
    // Given a value from RethinkDB, tries to infer its ReQL type.
    // Returns a string value, similar to r.typeOf result, or an empty
    // string if the type is not recognized or unsupported.
    switch (typeof value) {
        case "string":
            return "STRING";
        case "number":
            return "NUMBER";
        case "boolean":
            return "BOOL";
        case "null":
            return "NULL";
        case "object":
            // TODO: Implement check for PTYPE<GEOMETRY>
            if (_.isArray(value)) {
                return "ARRAY";
            } else if (_.isDate(value)) {
                return "PTYPE<TIME>";
            } else if (_.isTypedArray(value)) {
                return "PTYPE<BINARY>";
            } else {
                return "OBJECT";
            }
         default:
             return "";
     }
}

function spaceship(a, b) {
    // A simple three-way comparison ("spaceship operator") function.
    // Using JS built-in comparison logic, returns 0, -1 or 1,
    // depending on whenever values compare equal, less or greater.
    // Returns null if neither of comparisons succeed (non-comparable).
    if (a === b) {
        return 0;
    } else if (a < b) {
        return -1;
    } else if (a > b) {
        return 1;
    } else {
        return null;
    }
}

function compareValues(a, b) {
    // Compares two values in a (hopefully) same manner as RethinkDB would do.
    // Returns 0, -1 or 1 (see `spaceship` function) or null if cannot compare.

    /* if (typeof a === "string" && typeof b === "string") {  // Uncomment this to experiment with fast-path for strings
        return a === b ? 0 : (a < b ? -1 : 1);
    } */

    const ta = inferTypeOf(a),
          tb = inferTypeOf(b);

    if (ta === "" || tb === "") {
        return null;
    }
    if (ta !== tb) {
        return spaceship(ta, tb);
    }

    switch (ta) {
        case "STRING":
        case "NUMBER":
        case "BOOL":
        case "NULL":
            return spaceship(a, b);
        case "PTYPE<TIME>":
            return spaceship(a.getTime(), b.getTime());
        case "PTYPE<BINARY>":
            return null;  // unsupported
        case "ARRAY":
            for (let pair of _.zip(a, b)) {
                if (pair[0] === undefined) {
                    return -1;
                } else if (pair[1] === undefined) {
                    return 1;
                } else {
                    const c = compareValues(pair[0], pair[1]);
                    if (c !== 0) {
                        return c;
                    }
                }
            }
            return 0;
        case "OBJECT":
            return compareValues(_.toPairs(a).sort(), _.toPairs(b).sort());
        default:
            return null;
    }
}

module.exports = compareValues;

test.js

const timeit = require("timeit");
const uuidV4 = require('uuid/v4');
const compareValues = require("./index.js");


function usingCompareValues(done) {
    const a = uuidV4(), b = uuidV4();
    var res = compareValues(a, b);
    done();
    return res;
}

function usingJSComparison(done) {
    const a = uuidV4(), b = uuidV4();
    var res = a === b ? 0 : (a < b ? -1 : (a > b ? 1 : null));
    done();
    return res;
}


timeit.howlong(300000, [usingCompareValues, usingJSComparison], function (err, results) {
    console.log('Baseline', results[0]);
    console.log('Using compareValues', results[1]);
    console.log('Using JS comparison', results[2]);
});

Took a quick look, and I have to say this looks much better!

Great work. It is very easy to follow the logic in my head with this code.

I haven't tested this yet, but assuming everything works like it says on the tin, I may be able to merge this eventually.

Would you mind Submitting a new separate PR with this?

If so I will merge it into a separate testing branch in the main project.

@internalfx Sorry, haven't noticed your comments here earlier. I've created a PR, internalfx/thinker#11