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jashkenas--coffeescript/documentation/sections/splats.md
Geoffrey Booth 704924c3cd 2.0.0-beta3 (#4594)
* Don’t confuse the syntax highlighter

* Comment Assign::compilePatternMatch a bit

* Assignment expressions in conditionals are a bad practice

* Rename `wrapInBraces` to `wrapInParentheses`, to set the stage for future `wrapInBraces` that uses `{` and `wrapInBrackets` that uses `[`

* Correct comment

* object destructuring

* Allow custom position of the rest element.

* Output simple array destructuring assignments to ES2015

* Output simple object destructured assignments to ES2015

* Compile shorthand object properties to ES2015 shorthand properties

This dramatically improves the appearance of destructured imports.

* Don’t confuse the syntax highlighter

* Comment Assign::compilePatternMatch a bit

* Assignment expressions in conditionals are a bad practice

* Rename `wrapInBraces` to `wrapInParentheses`, to set the stage for future `wrapInBraces` that uses `{` and `wrapInBrackets` that uses `[`

* object destructuring

* Allow custom position of the rest element.

* rest element in object destructuring

* rest element in object destructuring

* fix string interpolation

* merging

* fixing splats in object literal

* Rest element in parameter destructuring

* merging with CS2

* merged with CS2

* Add support for the object spread initializer. https://github.com/tc39/proposal-object-rest-spread/blob/master/Spread.md

* Fix misspellings, trailing whitespace, other minor details

* merging with beta2

* refactor object spread properties

* small fix

* - Fixed object spread function parameters.
- Clean up "Assign" and moved all logic for object rest properties in single method (compileObjectDestruct).
- Add helper function "objectWithoutKeys" to the "UTILITIES" for use with object rest properties,
  e.g. {a, b, r...} = obj => {a, b} = obj, r = objectWithoutKeys(...)
- Clean up "Obj" and moved all logic for object spread properties in single method (compileSpread).
- Clean up "Code".
- Add method "hasSplat" to "Obj" and "Value" for checking if Obj contains the splat.
- Enable placing spread syntax triple dots on either right or left, per #85 (https://github.com/coffeescript6/discuss/issues/85)

* Fixed typos

* Remove unused code

* Removed dots (e.g. splat) on the left side from the grammar

* Initial release for deep spread properties, e.g. obj2 = {obj.b..., a: 1} or {obj[b][c]..., d: 7}
Tests need to be prepared!

* 1. Object literal spread properties

Object literals:
- obj = { {b:{c:{d:1}}}..., a:1 }

Parenthetical:
- obj = { ( body ), a:1 }
- obj = { ( body )..., a:1 }

Invocation:
- obj = { ( (args) -> ... )(params), a:1 }
- obj = { ( (args) -> ... )(params)..., a:1 }
- obj = { foo(), a:1 }
- obj = { foo()..., a:1 }

2. Refactor, cleanup & other optimizations.

* Merged with 2.0

* Cleanup

* Some more cleanup.

* Fixed error with freeVariable and object destructuring.

* Fixed errors with object spread properties.

* Improvements, fixed errors.

* Minor improvement.

* Minor improvements.

* Typo.

* Remove unnecessary whitespace.

* Remove unnecessary whitespace.

* Changed few "assertErrorFormat" tests since parentheses are now allowed in the Obj.

* Whitespace cleanup

* Comments cleanup

* fix destructured obj param declarations

* refine fix; add test

* Refactor function args ({a, b...})

* Additional tests for object destructuring in function argument.

* Minor improvement for object destructuring variable declaration.

* refactor function args ({a, b...}) and ({a, b...} = {}); Obj And Param cleanup

* fix comment

* Fix object destructuring variable declaration.

* more tests with default values

* fix typo

* Fixed default values in object destructuring.

* small fix

* Babel’s tests for object rest spread

* Style: spaces after colons in object declarations

* Cleanup comments

* Simplify Babel tests

* Fix comments

* Fix destructuring with splats in multiple objects

* Add test for default values in detsructuring assignment with splats

* Handle default values when assigning to object splats

* Rewrite traverseRest to fix handling of dynamic keys

* Fix double parens around destructuring with splats

* Update compileObjectDestruct comments

* Improve formatting of top-level destructures with splats and tidy parens

* Added a bigger destructuring-with-defaults test and fixed a bug

* Refactor destructuring grammar to allow additional forms

* Add a missing case to ObjSpreadExpr

* These tests shouldn’t run in the browser

* Fix test.html

* Fix docs scroll position getting screwed up by CodeMirror initialization

* Breaking change documentation about => (fixes #4593)

* Spread/rest syntax documentation

* Documentation about bound class methods

* 2.0.0-beta3 changelog

* Add note about ‘lib’

* Fix accidentally converting this to tabs

* Bump version to 2.0.0-beta3

* Update annotated source and test.html
2017-06-30 09:58:05 -07:00

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Splats, or Rest Parameters/Spread Syntax

The JavaScript arguments object is a useful way to work with functions that accept variable numbers of arguments. CoffeeScript provides splats ..., both for function definition as well as invocation, making variable numbers of arguments a little bit more palatable. ES2015 adopted this feature as their rest parameters.

codeFor('splats', true)

Splats also let us elide array elements...

codeFor('array_spread', 'all')

...and object properties.

codeFor('object_spread', 'JSON.stringify(currentUser)')

In ECMAScript this is called spread syntax, and has been supported for arrays since ES2015 but is coming soon for objects. Until object spread syntax is officially supported, the CoffeeScript compiler outputs the same polyfill as Babels rest spread transform; but once it is supported, we will revise the compilers output. Note that there are very subtle differences between the polyfill and the current proposal.