hello-world: simplify to unconditional "Hello, World!"

[petertseng]

The introductory exercise should require as little Rust knowledge as
necessary. We'd like to introduce cargo test here since it will be
used for all exercises, but introducing Option is too much.

exercism/problem-specifications#520

---

I wouldn't recommend merging this until the corresponding change is made in x-common.
Let's get it ready to go before then.

[ijanos]

I'm in favour of simplification but looking at this got me thinking. Strings in rust are not simple, while the classic tutorial work with a simple println!("Hello, world!"); here we have to call .to_string() or .into() or String::from() to satisfy the test.

If the purpose of this exercise is just to test that everything works then I'm starting to lean in the direction to use a primitive type here, a bool could work with something like this:

pub fn everything_works() -> bool {
    true
}

At this point however we have no connection to the common description. So another approach could be accepting a static string slice in the test. No conversion to String required but the type signature could be confusing or hard to guess if we don't provide a stub.

pub fn hello() -> &'static str {
    "Hello, World!"
}

Thoughts?

[petertseng]

Hmm, good point. I would say there are various measures we can take to lighten the load. We might combine some of these measures:

• static str, so we don't have to do to_string
• provide a stub
• provide a failing implementation that says "Goodbye, world" - then the student only has to change the Goodbye to Hello, should give the idea.

[petertseng]

Let's take all three. Note that using &'static str did not require any change to the test.

[ijanos]

I'm OK with this version. Maybe add a comment to the stub with this info: "the type of the return value looks funny because it has a static lifetime, this is a rust feature, dont mind it now"

[petertseng]

OK, take a look at that comment. Feel free to suggest changes to the wording.

[ijanos]

Looks good to me, but keep in mind that I am not a native English speaker :)

[petertseng]

Also removed Some/None from the config.json for hello-world.