repl: assign underscore fix by thefourtheye · Pull Request #3737 · nodejs/node

thefourtheye · 2015-11-10T16:26:11Z

As _ is not defined in REPL's context, when it is defined as const,
it breaks REPL, as it tries to store the result of the last evaluated
expression in _. This patch makes sure that _ is pre-defined in
REPL's context, so that if users define it again, they will get error.

This patch has a test to make sure that the REPL doesn't allow
redefining _ as const, also still assiging values to _ is
permitted.

Refer: #3729
Refer: #3704

cc @jasnell @cjihrig @targos @SamuelMarks @Fishrock123

cjihrig · 2015-11-10T16:30:12Z

Instead of referring to an issue, how about just explaining why we're doing this.

Adding here as well.

+1 to @cjihrig's comment. The reference to the issue is unnecessary, I think.

cjihrig · 2015-11-10T16:32:50Z

In the docs, where it says The special variable _ (underscore) contains the result of the last expression., maybe add another sentence saying that attempting to create a const _ variable will fail.

thefourtheye · 2015-11-10T16:41:12Z

@cjihrig Did you mean to leave that comment in #3729?

thefourtheye · 2015-11-10T16:43:49Z

@cjihrig Updated as per the suggestions. PTAL.

cjihrig · 2015-11-10T20:48:23Z

Can you add "the" between "in" and "REPL."

cjihrig · 2015-11-10T20:51:04Z

A couple small comments, but LGTM. Once the CI is fully available, feel free to squash this and run the tests.

targos · 2015-11-10T20:55:14Z

typo: redefinitions

jasnell · 2015-11-12T19:43:19Z

LGTM sans a few minor comments.

jasnell · 2015-11-13T20:18:26Z

@thefourtheye ... can you please rebase and update?

As `_` is not defined in REPL's context, when it is defined as `const`, it breaks REPL, as it tries to store the result of the last evaluated expression in `_`. This patch makes sure that `_` is pre-defined in REPL's context, so that if users define it again, they will get error. Refer: nodejs#3729 Refer: nodejs#3704

If the `_` is redefined as `const` in REPL, it will break the REPL, as REPL will store the result of the last evaluated expression in `_`. This patch has a test to make sure that the REPL doesn't allow redefining `_` as `const`, also still assiging values to `_` is permitted. Refer: nodejs#3729 Refer: nodejs#3704

When users assign a value to `_` in REPL, it is prone to unexpected results or messing up with REPL's internals. For example, nodejs#3704. This patch issues a warning about the same.

thefourtheye · 2016-02-25T21:29:45Z

Sorry for the delay. I updated and rebased now. PTAL.

thefourtheye · 2016-02-25T21:30:14Z

CI Run: https://ci.nodejs.org/job/node-test-pull-request/1754/

jasnell · 2016-03-02T17:32:39Z

LGTM

jasnell · 2016-03-22T06:03:49Z

Closing given that #5535 landed.

thefourtheye added the repl Issues and PRs related to the REPL subsystem. label Nov 10, 2015

cjihrig reviewed Nov 10, 2015
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cjihrig mentioned this pull request Nov 10, 2015
doc: warn about reassigning _ in REPL #3729
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thefourtheye force-pushed the repl-assign-underscore-fix branch from c5273ff to 3d8bb15Compare November 10, 2015 16:43

cjihrig reviewed Nov 10, 2015
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Can you add "the" between "in" and "REPL."

targos reviewed Nov 10, 2015
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typo: redefinitions

jasnell added lts-watch-v4.x and removed lts-watch-v4.x labels Nov 12, 2015

Trott force-pushed the master branch from 1e896a6 to 082cc8dCompare December 27, 2015 02:01

thefourtheye force-pushed the repl-assign-underscore-fix branch from 63b27a6 to 71fe0a9Compare February 25, 2016 21:10

thefourtheye added 3 commits February 26, 2016 02:57

doc: warn about reassigning _ in REPL
48d79a4
When users assign a value to `_` in REPL, it is prone to unexpected results or messing up with REPL's internals. For example, nodejs#3704. This patch issues a warning about the same.

thefourtheye force-pushed the repl-assign-underscore-fix branch from 71fe0a9 to 48d79a4Compare February 25, 2016 21:28

rvagg mentioned this pull request Feb 26, 2016
repl: warn on assignment to _ #5438
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jasnell added the lts-watch-v4.x label Mar 2, 2016

jasnell closed this Mar 22, 2016

thefourtheye deleted the repl-assign-underscore-fix branch March 22, 2016 06:09

MylesBorins removed the lts-watch-v4.x label Mar 23, 2016

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