How would we copy... Anything?
On Mon, Feb 23, 2015 at 10:10 AM, Michał Wadas <michalwadas at gmail.com> wrote:
My proposition is to create a new well known Symbol - Symbol.clone and corresponding method on Object - Object.clone.
Anything that does not deal with dslomov-chromium/ecmascript-structured-clone should not be considered.
Le 23/02/2015 10:10, Michał Wadas a écrit :
Cloning objects is long requested feature. "clone object javascript" yields 1 480 000 results in Google.
I'd like to share this as an answer facebook.github.io/immutable-js/#the-case-for-immutability "If an object is immutable, it can be "copied" simply by making another reference to it instead of copying the entire object. Because a reference is much smaller than the object itself, this results in memory savings and a potential boost in execution speed for programs which rely on copies (such as an undo-stack)."
var map1 = Immutable.Map({a:1, b:2, c:3});
var clone = map1;
Despite people saying all over the Internet they want cloning, maybe they want immutability?
Primitives are cloned easily.
Primitives are immutable, no need to clone them. If you're referring to "primitive objects", it might be better to forget about this weird corner of the language than polish it.
Back to something you wrote above:
Users are encorauged to define their own Symbol.clone logic.
Perhaps this cloning protocol can be purely implemented in userland as a library and doesn't need support from the language. That's one of the reasons symbols have been introduced after all.
I'm aware about structured clone, but there is a basic difference - structured clone is a way to copy object to other Realm, Symbol.clone would be a more powerful (supporting constructors, classes and functions) way to clone objects.
On 23 February 2015 at 10:37, David Bruant <bruant.d at gmail.com> wrote:
Le 23/02/2015 10:10, Michał Wadas a écrit :
Cloning objects is long requested feature. "clone object javascript" yields 1 480 000 results in Google.
I'd like to share this as an answer facebook.github.io/immutable-js/#the-case-for-immutability "If an object is immutable, it can be "copied" simply by making another reference to it instead of copying the entire object. Because a reference is much smaller than the object itself, this results in memory savings and a potential boost in execution speed for programs which rely on copies (such as an undo-stack)."
var map1 = Immutable.Map({a:1, b:2, c:3}); var clone = map1;
To be clear, that is only true in general as long as immutable objects also don't have identity. With identity (i.e., reference equality), the difference between an alias and an actual copy is still observable. JavaScript is plagued by all objects having identity, a well-known problem preventing various optimisations in compilers.
In other words, the ES spec would have to make an explicit and conscious decisions to say that "cloning" an immutable object is not actually cloning it. A compiler or runtime system usually cannot apply that decision itself (except for primitives, which have structural equality).
Despite people saying all over the Internet they want cloning, maybe they want immutability?
Yeah, I tend to agree with that sentiment.
Cloning objects is long requested feature. "clone object javascript" yields 1 480 000 results in Google.
My proposition is to create a new well known Symbol - Symbol.clone and corresponding method on Object - Object.clone.
Default behavior for an object is to throw on clone try.
Object.prototype[Symbol.clone] = () => { throw TypeError; }Users are encorauged to define their own Symbol.clone logic.
Primitives are cloned easily.
Number.prototype[Symbol.clone] = String.prototype[Symbol.clone] = Boolean.prototype[Symbol.clone] = function() {return this.valueOf();}Sets, Dates, Maps, WeakMaps, WeakSets have cloned their internal state. Set.prototype[Symbol.clone] = function() {return new Set(this);} (cloning WeakMap or WeakSet isn't possible in ES6 code anyway)
Every object returned from JSON.parse can be cloned if all it's subnodes are clonable.
Arrays can be cloned if all it's items are clonable.
Moreover, it can be used as future way to clone iterators.
Cloning objects is long requested feature. "clone object javascript" yields 1 480 000 results in Google. My proposition is to create a new well known Symbol - Symbol.clone and corresponding method on Object - Object.clone. Default behavior for an object is to throw on clone try. Object.prototype[Symbol.clone] = () => { throw TypeError; } Users are encorauged to define their own Symbol.clone logic. Primitives are cloned easily. Number.prototype[Symbol.clone] = String.prototype[Symbol.clone] = Boolean.prototype[Symbol.clone] = function() {return this.valueOf();} Sets, Dates, Maps, WeakMaps, WeakSets have cloned their internal state. Set.prototype[Symbol.clone] = function() {return new Set(this);} (cloning WeakMap or WeakSet isn't possible in ES6 code anyway) Every object returned from JSON.parse can be cloned if all it's subnodes are clonable. Arrays can be cloned if all it's items are clonable. Moreover, it can be used as future way to clone iterators.