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Showing content from https://github.com/tc39/proposal-optional-chaining/issues/18 below:

Should we include “optional property assignment” a?.b = c · Issue #18 · tc39/proposal-optional-chaining · GitHub

For the most general case illustrating short-circuiting, the instruction:

is equivalent to:

if (a != null)
    a.b.c().d = e;

@alangpierce has found real-world usages of that form in CoffeeScript, some of them seem reasonable, including two-level deep chains a?.b.c = d:
https://gist.github.com/alangpierce/34b7aa40cda51b0a089a44680bdfed7e

Should we include that? In particular, are the semantics clear enough? There are the following subcases:

• simple assignment: a?.b = c
• combined assignment: a?.b += c, a?.b >>= c, etc.
• increment/decrement: a?.b++, --a?.b, etc.
• destructuring assignment: { x: a?.b } = c, [ a?.b ] = c, etc.
• for-in/of loop header: for (a?.b in c), for (a?.b of c)

stefnotch, himynameisdave, afshin-hoseini, harryadel, tjdavies and 38 more

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