Apply clone option to target object #209

creativeux · 2020-10-29T03:14:13Z

closes #208
closes #186

Added ternary for initializing the destination object based on the clone option.
Added 2 unit tests... 1 to test that target type info is retained, and another to ensure that target memory pointer is maintained when clone is set to false.

TehShrike · 2020-10-29T16:01:15Z

This looks good. One request – could you add a test that asserts that when merge.all is called with { clone: true }, the first element is mutated/returned?

creativeux · 2020-10-29T17:13:47Z

could you add a test that asserts that when merge.all is called with { clone: true }, the first element is mutated/returned?

Great call, I hadn't used that entrypoint so didn't think to change it. I made the change, but it required a few more lines to change to make it elegant and aligned with the code style in place. The firstArrayEntry() method is there to avoid chained ternaries which can be confusing to read, and I moved the logic to determine if the destination should be a new object or a target object into a function.

Let me know if you'd like any add'l changes!

RebeccaStevens · 2020-10-29T22:49:15Z

I like it but I am a little worried about backwards compatibility. As is, this would definitely need to be released as a new major version.

creativeux · 2020-10-29T23:18:34Z

I like it but I am a little worried about backwards compatibility. As is, this would definitely need to be released as a new major version.

You're probably right. This is an awkward one because it sounds like it is technically a bug fix because the API "lies" to the consumer about how the clone option is applied, but fixing it potentially breaks consumers whose code relies on the bug being there. I'll let you guys duke it out 😉

TehShrike · 2020-10-30T00:04:44Z

Yup, this would be a breaking change. I'm thinking to pair it with removing the deprecation warning from the clone flag

RebeccaStevens · 2020-11-06T03:41:15Z

~~I've changed my mind on liking this.~~ [I'm back to liking it now]

I like the idea behind it but this is definitely a breaking change that I can see a lot of push back happening on if it goes live.

The current implementation of the clone flag makes it so that if set to false, objects will be directly copied over to the resulting merged object.
The new behavior in this MR as is makes it so that when the clone flag is false, the target option will be mutated.

These two behaviors are very different and I don't think it would be a good idea to switch from one to the other using the same flag.

The issue with having this behavior on the "clone" flag is that it that it is valid to want to both clone and not mutate the any of the parameters.

I would be best to put this behavior behind a new flag called "mergeWithTarget".

I just made a new issue #212 with my proposal for the clone behavior.

creativeux · 2020-11-06T04:03:29Z

@RebeccaStevens I lied about how long it would take. My wife started watching The Bachelorette and that was my cue to zone out. Let me know if this addresses the concerns re: clone vs mergeWithTarget.

index.js

RebeccaStevens · 2020-11-06T04:42:21Z

Looks good to me 👍

RebeccaStevens · 2020-11-06T04:49:40Z

@creativeux do you want to mark this as closes #186?

creativeux · 2020-11-06T05:03:57Z

index.js

@@ -51,8 +55,17 @@ function propertyIsUnsafe(target, key) {
 			&& Object.propertyIsEnumerable.call(target, key)) // and also unsafe if they're nonenumerable.
 }

+// Retrieves either a new object or the appropriate target object to mutate.
+function getDestinationObject(target, options) {
+	if (options && options.mergeWithTarget) {


@RebeccaStevens does this need to account for options.clone scenarios for objects that are not the root target? I've read through it a few times and with deepmerge being self-referenced, I wonder if there's a case where this function would be called in reference to an object nested deeper than the entrypoint where we might want to return the target here in the case where options.clone is false?

No I don't think so. This function is only called at most once per call of the main deepmerge function.

Per my last commit, this is called repeatedly during recursion down an object tree. Not sure if this changes your thought on the topic.

Specifically, deepmerge is returned from cloneUnlessOtherwiseSpecified which can call mergeObject which calls getDestinationObject.

I think I'm seeing the issue you are talking about here.

~~I think with options.mergeWithTarget: true & options.clone: false, merging with each target going down should happen.~~
~~I think with options.mergeWithTarget: true & options.clone: true, merging should only happen with the top most target.~~

Actually no, scrap that. Merging should only ever happen with the top most target.

Looking at the codebase, it doesn't really look set up to be able to add this functionality easily in a non-hacky way.
A bunch of refactoring may be needed (which I'm in the process of doing in #215).

If you want to just do it in a hacky way, you could just remove mergeWithTarget from the options object before it is passed to the recursive call.

creativeux · 2020-11-12T19:44:22Z

@TehShrike and @RebeccaStevens - I caught a bug with my in-use fork of this where the merge fails in the case that a target is undefined. I pushed a fix and a unit test to ensure that there is always an emtpy object or array to merge into if the target is undefined.

RebeccaStevens · 2020-11-12T21:32:46Z

index.js

+		return Array.isArray(target) ? firstArrayEntry(target) : target
+	}
+
+	return isArray ? [] : {};


The destination object should never be an array.

This is how I would define this function:

function getDestinationObject(target, options) { const targetDefined = typeof target !== 'undefined' const doMerge = options && (options.mergeWithTarget || options.clone === false) if (targetDefined && doMerge) { return target } return {}; }

Call from deepmergeAll

For me, the array check was required because during recursion it's possible that there is a property being handled whose value is undefined, but we know that the source value is an array, so we need to instantiate an empty object that can be merged into. If I remove this, nested properties with array types will fail to merge because an array source will try to be merged into an object target.

Yeah sorry, I was thrown off by the function mergeObject's name. I assumed that it's parameters were always non-array objects but in actual fact it merges any 2 values (or returns the latter one if they can't be merged).

Wait no, that's not right. mergeObject does only ever receive non-array objects. target and source should never be arrays in mergeObject - arrays should be handled by options.arrayMerge.

@creativeux I suspect you'll need to update the logic in deepmerge itself to handle the case of target being undefined.

https://github.com/TehShrike/deepmerge/blob/master/index.js#L87-L93

RebeccaStevens · 2020-11-12T21:34:59Z

index.js

@@ -100,7 +117,7 @@ deepmerge.all = function deepmergeAll(array, options) {

 	return array.reduce(function(prev, next) {
 		return deepmerge(prev, next, options)
-	}, {})
+	}, getDestinationObject(array, undefined, options))


Following on from my other comment, this is how getDestinationObject would be called from deepmergeAll:

const target = array[0]; const destination = getDestinationObject(target, options) const source = destination === target ? array.slice(1) : array return source.reduce(function(prev, next) { return deepmerge(prev, next, options) }, destination)

Apply clone option to target object

97833ed

Apply target mutation to merge.all first array entry

b9020e0

Aaron Stone added 2 commits October 29, 2020 11:15

Missing index on return

10deb35

Index madness. Oops.

38d54b2

RebeccaStevens mentioned this pull request Nov 6, 2020

New "clone" behavior #212

Open

Aaron Stone added 2 commits November 5, 2020 20:58

Add cloneWithTarget flag

cf8ef25

merge with target, not clone with target...

971f5e6

RebeccaStevens reviewed Nov 6, 2020

View reviewed changes

index.js Outdated Show resolved Hide resolved

Remove unnecessary boolean cast

c5688b7

creativeux commented Nov 6, 2020

View reviewed changes

Handle undefined target

3b66e4c

RebeccaStevens reviewed Nov 12, 2020

View reviewed changes

creativeux force-pushed the clone-target-false branch from 2ae7430 to 3b66e4c Compare November 12, 2020 23:45

Aaron Stone added 2 commits November 13, 2020 16:32

Improve undefined source / target testing

dadd37e

Incomplete assertion definitions

4c0d549

TehShrike mentioned this pull request Jan 20, 2021

Un-deprecate clone, make it not a liar about the root object #225

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Apply clone option to target object #209

Apply clone option to target object #209

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Apply clone option to target object #209

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Apply clone option to target object #209

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