libstd: replace all try! with ? in documentation examples

[utkarshkukreti]

See #38644.

For the record, I used the following Perl one-liner and then manually fixed a couple of things it got wrong:

$ perl -p -i -e 's#(///.*)try!\((.*)\)#$1$2?#' src/libstd/**/*.rs

[rust-highfive]

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[utkarshkukreti]

r? @steveklabnik

[steveklabnik]

/cc @rust-lang/docs , I would like more than one person to review this PR, as it's very long and tedious, which means that we're likely to miss something.

[durka]

Why not replace Many of the examples in this module use the [try!] macro with Many of the examples in this module use the [? operator] (and link to the Syntax Index, probably)?

[utkarshkukreti]

I don't think that information is really relevant in this module documentation, but I'd be happy to add what you suggested if others think the same. @steveklabnik?

[frewsxcv]

I don't think that documenting try! or ? is needed here, but I don't feel strongly.

[steveklabnik]

My inclination is to say that this PR should be about a fairly mechanical translation, so keeping it here is fine.

[utkarshkukreti]

Done!

[Stebalien]

I'd suggest manually converting many of the multi-line let a = try!(foo()); let b = try!(bar(a)); ... blocks of code with a()?.b()?.c()? expressions. This was a major motivation for introducing the question mark operator.

[utkarshkukreti]

@Stebalien I started doing that but found many cases in which I'm not sure if a single line would be clearer for the reader (I personally would write most of these in a single line in my code). For example, what do you (and others as well) think about converting these 2 cases into single lines:

let mut f = File::create("foo.txt")?;
f.write_all(b"Hello, world!")?;

-> File::create("foo.txt")?.write_all(b"Hello, world!")?;

and

let mut f = File::create("foo.txt")?;
f.set_len(10)?;

-> File::create("foo.txt")?.set_len(10)?;?

[steveklabnik]

or example, what do you (and others as well) think about converting these 2 cases into single lines:

I tend to generally write them as two lines.

That said, I think it's best to not mess too much with the formatting of the examples here, and just worry about the transformation. So let's

Thank you!

@bors: r+

[josephpd3]

As someone new to the syntax, I like the decision to keep things unchained for these examples. It seems clearer visually, given the context. Looks good @utkarshkukreti!

[pnkfelix]

its sort of a shame that one cannot link right to the ? operator within the index, but AFAICT there is no anchor for it specifically. (You could link to https://doc.rust-lang.org/stable/book/syntax-index.html#operators-and-symbols but I'm not sure if that pays off.)

[pnkfelix]

r=me, in case you still wanted a secondary reviewer @steveklabnik

[bors]

☔ The latest upstream changes (presumably #39176) made this pull request unmergeable. Please resolve the merge conflicts.

[frewsxcv]

It looks like the bors approval didn't go through for this PR for some reason (hence it not being merged yet). @utkarshkukreti If you get some time to address the merge conflicts, we can try again. Sorry about that

[utkarshkukreti]

@frewsxcv rebased!

[frewsxcv]

Thanks!

@bors r=pnkfelix,steveklabnik,frewsxcvx

[bors]

📌 Commit 19724d3 has been approved by pnkfelix,steveklabnik,frewsxcvx

[bors]

⌛ Testing commit 19724d3 with merge b79081c...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: pnkfelix,steveklabnik,frewsxcvx
Pushing b79081c to master...