Improve Concept Exercise: Type Conversion #1248

junedev · 2021-08-03T19:52:53Z

Closes #1247
Closes #947 (@SleeplessByte I diverged a bit from what you wrote there, hope that's ok for now.)

Notes

I don't cover the "behind the scenes" currently in about.md, e.g. boxed vs. non-boxed primitives, toPrimitive, details on toString. This is to save time right now but also because it is not clear to me yet whats the best place for this info in our concept tree.
I also don't cover all the weirdness currently, like object + string. Not sure how much value there is going into this tbh.
I replaced the third task because the old one didn't practice anything that wasn't already part of task 1 and 2. The new task now practices implicit conversion to boolean.
There are lots of places where I use MDN links currently but once we have more concepts of our own (e.g. on JSON) we could link to those.
No analyzer ideas yet in the design.md file, also to save some time before launch.

angelikatyborska · 2021-08-22T14:05:38Z

FYI the PR description references this PR with "closes", I think you meant to reference the issue #1247 instead?

junedev · 2021-08-22T14:10:08Z

Yes. 🙈 Fixed.

angelikatyborska

I read through everything and tried to solve the exercise in my head before looking up the hints. It all makes sense to me, I didn't find any problems. And I learned something!

angelikatyborska · 2021-08-22T14:17:32Z

concepts/type-conversion/about.md

+Boolean('0');
+// => true
+
+Boolean('false');
+// => true


I'm not much of a Polyglot but I'm curious which languages would consider those strings to be falsy?

In Ruby and Elixir, the concept of falsy is very limited, only 0 and nil are falsy.

On this page https://javascript.info/type-conversions#boolean-conversion they say '0' is falsy in PHP. 'false' is not really an example from another language, it is rather something that might be unexpected. I run into this last week when I wrote if (<some environment variable>). Then I was confused why the if block was still executed even though the environment variable was set to false. Anyway, I will use the phrasing from the introduction instead so people don't start wondering about which languages are meant here.

angelikatyborska · 2021-08-22T14:19:00Z

concepts/type-conversion/about.md

+Number(undefined);
+// => NaN


So Number(undefined) is NaN, but Number() is 0? 🤯

you are right but I didn't know this either 🤯

I added a sentence about this behavior. I couldn't find an explanation though.
@SleeplessByte Do you know what's going on there?

I do. It's specced

Number ( [ value ] ) Returns a Number value (not a Number object) computed by ToNumber(value) if value was supplied, else returns +0.

So this has a special case for no argument, which is +0.

Then we check ToNumber:

Argument Type Result

Undefined NaN

Null +0

Boolean The result is 1 if the argument is true. The result is +0 if the argument is false.

Number The result equals the input argument (no conversion).

String See grammar and note below.

Object Apply the following steps:Let primValue be ToPrimitive(input argument, hint Number).Return ToNumber(primValue).

and thus explicitly passing undefined is a different result (NaN) than passing nothing.

I got that part but I was wondering why it was specced that way.

Probably legacy / new String, new Array, new Number should be "the same" as in create an "empty" value of that type ('', [], and +0). It would be weird if that created a NaN. However passing in undefined makes it subject to coercion. Something like that.

concepts/type-conversion/about.md

angelikatyborska · 2021-08-22T14:22:38Z

concepts/type-conversion/about.md

+Another common way to achieve a better string representation for objects and arrays is to use [JSON encoding][json].
+
+```javascript
+const obj = {
+  name: 'Gilda Guerra',
+  address: {
+    city: 'Goiânia',
+  },
+};
+
+JSON.stringify(obj);
+// => '{"name":"Gilda Guerra","address":{"city":"Goiânia"}}'
+```


Should this text also mention JSON.parse?

I didn't want to dive too much into this because it will have a separate exercise/concept but I agree that if I show the one direction I should also mention the other way. I added a sentence to cover that.

angelikatyborska · 2021-08-22T14:28:04Z

concepts/type-conversion/about.md

+
+### String Context
+
+If the addition operator `+` is used for primitive values and one operand is a string, the other one will be coerced into a string as well (if necessary).


I think the "if necessary" is already implied by saying "one operand is a string". If only one of the is a string, it is necessary.

Suggested change

If the addition operator `+` is used for primitive values and one operand is a string, the other one will be coerced into a string as well (if necessary).

If the addition operator `+` is used for primitive values and one operand is a string, the other one will be coerced into a string as well.

fixed in all the places

exercises/concept/lucky-numbers/.docs/instructions.md

angelikatyborska · 2021-08-22T14:45:39Z

exercises/concept/lucky-numbers/.meta/config.json

@@ -1,6 +1,6 @@
 {
-  "blurb": "TODO: add blurb for lucky-numbers exercise",
-  "authors": ["shubhsk88"],
+  "blurb": "Practice type conversion while helping your friend Kojo with his website.",


I know blurbs are like "whatever", but... this one feels a bit weird to me because it doesn't have any connection to the exercise's name. Maybe:

Suggested change

"blurb": "Practice type conversion while helping your friend Kojo with his website.",

"blurb": "Practice type conversion while helping your friend Kojo with his website www.fun-with-numbers.com.",

fixed, I do think blurbs are important

junedev · 2021-08-22T20:15:24Z

@SleeplessByte I will merge this now. Feel free to also do another review here later if you want and I will create a PR with the fixes.

junedev added 17 commits August 3, 2021 21:50

fix link in conditionals concept

44b0735

some cleanup

91ef47a

Merge branch 'main' into improve-concept-exercise-type-conversion

116f5e9

add Number, Boolean, String section

1ab50dd

add parts of type coercion section

1267552

finish about.md

8377af1

finish concept part

dff6262

add story and exercise introduction

ffa30ac

add blurb

809edca

add new third task

983feba

fix exemplar solution

de6d8f8

update exemplar and instructions

605a0ee

fix hints

c259cc1

add design file

b7a63d5

fix configs etc

c672e8f

Merge branch 'main' into improve-concept-exercise-type-conversion

a13b396

format

856341d

junedev marked this pull request as ready for review August 21, 2021 13:02

junedev requested a review from a team August 21, 2021 13:03

small fixes

8744c5f

angelikatyborska approved these changes Aug 22, 2021

View reviewed changes

Merge branch 'main' into improve-concept-exercise-type-conversion

f129953

fixes according to review

3076570

junedev merged commit 15748ec into exercism:main Aug 22, 2021

junedev deleted the improve-concept-exercise-type-conversion branch August 22, 2021 20:15

This was referenced Jul 14, 2022

Document reputation label exercism/docs#347

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Consider correct reputation amounts for different labels exercism/exercism#6440

Open

Consider correct reputation amounts for different labels exercism/exercism#6441

Closed

Argument Type	Result
Undefined	NaN
Null	+0
Boolean	The result is 1 if the argument is true. The result is +0 if the argument is false.
Number	The result equals the input argument (no conversion).
String	See grammar and note below.
Object	Apply the following steps:Let primValue be ToPrimitive(input argument, hint Number).Return ToNumber(primValue).


		### String Context

		If the addition operator `+` is used for primitive values and one operand is a string, the other one will be coerced into a string as well (if necessary).

	"blurb": "Practice type conversion while helping your friend Kojo with his website.",
	"blurb": "Practice type conversion while helping your friend Kojo with his website www.fun-with-numbers.com.",

		Number(undefined);
		// => NaN

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Improve Concept Exercise: Type Conversion #1248

Improve Concept Exercise: Type Conversion #1248

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angelikatyborska commented Aug 22, 2021

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junedev commented Aug 22, 2021

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junedev commented Aug 3, 2021 •

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