[Sept Sprint] New exercise teaching type-conversion

[ErikSchierboom]

This is part of our September Spring to get the Go Track in shape. Please read the Overview issue for more details. This exercise is claimed by @jmrunkle.

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Before building this exercise (or exercises), please read up on the documentation.

We need an exercise for the type-casting and type-assertions concepts. Since there is sometimes confusion around those two things, it makes sense to teach both in the same exercise to demonstrate how they are related.

If it makes sense, this exercise could also teach about the type-switch concept.

The exercise should teach:

• How to convert from one type to another
• How to assert a type
• How to assert an interface type

This exercise will have at least interfaces as a prerequisite.

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Remaining work:

• sorting-room: fill out type-conversion concept documentation #1702
• sorting-room: fill out type-assertion concept documentation #1703
• sorting-room: teach about type-switch syntax #1704

[ErikSchierboom]

See https://github.com/exercism/go/blob/ed630183cccef21791ca21da0ecaafc5b52f9118/exercises/concept/cars-assemble/.docs/introduction.md#type-conversion for the original type conversion introduction text.

[jmrunkle]

This is blocked on #1638. Until then we cannot add an exercise that requires the interfaces concept. We can add it as status: "wip", but configlet will complain if you try to enable the new concept exercise since its prereq is not taught by some exercise.

[jmrunkle]

I would be happy to take this one, but I am having trouble coming up with a good story for this one. I looked at the canonical stories list (https://exercism.org/docs/building/tracks/stories), but nothing jumped out at me.

The best I could come up with is you have some kind of sorting room which has to handle anything that is put in there. Some things have predefined results (eg. "This is a number" or "This is a string"), but a few things need to be unpacked and have their contents inspected (eg. "This is a box containing a number 4"). Anything unexpected will be marked "Return to sender".

If no one has a better story I can get rolling with that.

I'll probably start with a PR just to fix the actual concept documentation for type-conversion and type-assertion which is nothing but TODOs right now. I can also add the type-switch concept which seems pretty relevant here.

[ErikSchierboom]

I think that story could work fine. Maybe you could make it Santa themed and have the boxes be presents or something like that?

[jmrunkle]

I was already pretty far into the implementation by the time I saw your comment there Erik so I am probably just moving forward with the sorting room idea rather than trying to refactor it to be about Santa. For the record, here is what the intro looks like so far:

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Jen is working in the sorting room in a large factory. The sorting room needs to process anything that comes into it by categorizing it with a label. She needs a program to help her with the sorting.

Most primitive values should get straight-forward labels. For numbers, she wants strings saying "This is the number 2.0" (if the number was 2). Jen wants the same output for integers and floats. For booleans, she wants strings saying "This is false" or "This is true".

There are a few Box interfaces that need to be unwrapped to get their contents. For a NumberBox, she wants strings saying "This is a box containing the number 3.0" (if the Number() method returns 3). For a BooleanBox, she wants strings saying "This box is true" or "This box is false" (depending on the result from the Boolean() method).

Anything unexpected should say "Return to sender" so Jen can send them back where they came from.

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Seems to work well enough and gives me enough space to get the ideas across. I am sure there will be more discussion over in the pull request itself.

[junedev]

tbh I think a neutral theme is better than something related to a christian holiday that does not exist in some cultures

[ErikSchierboom]

True. The sorting room is perfectly fine.

[jmrunkle]

Woot, got that one out the door!

[ErikSchierboom]

Sweet!