`isObject` should not allocate

What is the Problem Being Solved?

Marshaling uses isObject on every marshalled element to determine whether it needs to be handled specially. The current test is robust against future changes to the JS spec, but allocates in most circumstances. As a result, the test is (expected to be) horrifically expensive.

Description of the Design

We use isObject so that we can change that test in one place. We should take advantage of that now to make the test non-allocating given the current JS spec. Change it to

export const isObject = val => val !== null &&  typeof val === 'object' || typeof val === 'function';

For usability, we should also add isPrimitive as the dual of isObject. Many uses would be much more readable as a result.

Security Considerations

The test must be updated if future versions of the language add more typeof cases that are not primitives.

Test Plan

Rerun tests with the isObject definition changed.

[mhofman]

Here are 2 variations of a suggestion, that should be as safe as the current always allocating Object(value) === value:

const isObject = value => {
  switch (typeof value) {
    case 'undefined':
      // [[IsHTMLDDA]]
      return value !== undefined;
    case 'boolean':
    case 'number':
    case 'string':
    case 'bigint':
    case 'symbol':
      return false;
    default:
      return value !== null && Object(value) === value;
  }
};

or

const knownSafePrimitives = freeze({
  __proto__: null,
  boolean: true,
  number: true,
  string: true,
  bigint: true,
  symbol: true,
  undefined: false,
  object: false,
  function: false,
});
const isObject = value =>
  !knownSafePrimitives[typeof value] &&
  value !== undefined && // [[IsHTMLDDA]] has typeof 'undefined'
  value !== null && // null has typeof 'object'
  Object(value) === value;

[kriskowal]

Please reopen if I’ve misunderstood the substance of the conversation above.

My understanding from above benchmark is that isObject proves to be the fastest option on both XS and V8 of all the options that are safe in the face of language change. Between Endo and Agoric SDK, we define isObject in ses and marshal and they are both already sorted.

• ses https://github.com/endojs/endo/blob/c9b1909e3aa128a6d01f862b9d513237ad45d1a1/packages/ses/src/commons.js#L252
• marshal https://github.com/endojs/endo/blob/c9b1909e3aa128a6d01f862b9d513237ad45d1a1/packages/marshal/src/helpers/passStyle-helpers.js#L20

Thank you @gibson042. Benchmarks are full of surprises!