destructuring - caffeine-suite/caffeine-script GitHub Wiki

See also: Structuring and Restructuring

1. Extract-Destructuring: a extract b. Extract is more capable and uses less syntax. Extract returns the last value extracted.
2. Assignment-Destructuring: {b} = a. Assignment-Destructuring's return-value supports Restructuring.

Assignment-style will feel familiar to JavaScript and CoffeeScript veterans. With the exception of the return-value, assignment-style is identical to JavaScript ES6 Destructuring Assignment, and is a subset of CoffeeScript Destructuring Assignment.

CoffeeScript and Javascript, as of EcmaScript6 (ES6), have "destructuring assignment." At first it seems cool and elegant, but after using it for a few years, I've found it awkward and largely ineffective in all but the simplest cases:

One of CaffeineScript's core goals is Eliminating Bracket Matching.

Nesting ends up taking more tokens than the simpler, old-school, non-pattern assignment.

# Assignment-destructuring:
{a:{b}} = c    # 8 tokens

# old-school
b = a.c        # 5 tokens

# CaffeineScript's `extract`
a extract b extract c  # 5 tokens

Why? Data-flow actually changes directions. In assignment, data flows right-to-left:

  {a} = c
#  ^----/           # right-to-left data-flow

But in with nested assignment-destructuring, data flows left-to-right:

  {a:{b}} = c  
#  /--^             # left-to-right data-flow
#  \--------/       # right-to-left data-flow

With extract, data always flows left-to-right:

a extract b
a extract b extract c

CoffeeScript/JavaScript destructuring returns the object being destructured. I have never found that useful. Instead, I usually want the extracted value returned, usually for testing in an if-statement if it is present. In CaffeineScript, instead of one (almost) useless return value, you have two, equally useful options:

• a extract b, c returns c, the last value extracted
• {b, c} = a returns a new object: {b, c}, destructuring-Assignment's return-value, if used, provides Restructuring