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Support InMemoryCache({ freezeResults: true }) to help enforce immutability. #4514

Merged
merged 3 commits into from
Feb 28, 2019
Merged

Support InMemoryCache({ freezeResults: true }) to help enforce immutability. #4514

merged 3 commits into from
Feb 28, 2019

Commits on Feb 28, 2019

  1. Support InMemoryCache({ freezeResults: true }) to help enforce immuta… 

    …bility.

Part of the plan I outlined in this comment:
#4464 (comment)

If we could trust application code not to modify cache results, we
wouldn't have to save deep snapshots of past results in order to implement
isDifferentFromLastResult correctly (see #4069).

Aside: why doesn't the cache just return defensive copies of all results?
#4031 (comment)

While you might agree that immutability is a worthwhile aspiration, it can
be hard to maintain that discipline across your entire application over
time, especially in a team of multiple developers.

This commit implements a new freezeResults option for the InMemoryCache
constructor, which (when true) causes all cache results to be frozen in
development, so you can more easily detect accidental mutations.

Note: mutating frozen objects only throws in strict mode, whereas it fails
silently in non-strict code. ECMAScript module code automatically runs in
strict mode, and most module transforms add "use strict" at the top of the
generated code, so you're probably already using strict mode everywhere,
though you might want to double-check.

The beauty of this implementation is that it does not need to repeatedly
freeze entire results, because it can shallow-freeze the root of each
subtree when that object is first created.

Thanks to result caching, those frozen objects can be shared between
multiple different result trees without any additional freezing, and the
entire result always ends up deeply frozen.

The freezing happens only in non-production environments, so there is no
runtime cost to using { freezeResults: true } in production. Please keep
this in mind when benchmarking cache performance!
    @benjamn
    benjamn committed Feb 28, 2019
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  2. Bump bundle size limit for apollo-cache-inmemory.

    @benjamn
    benjamn committed Feb 28, 2019
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  3. Mention PR #4514 in CHANGELOG.md.

    @benjamn
    benjamn committed Feb 28, 2019
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