Add method str::repeat(self, usize) -> String

[bluss]

It is relatively simple to repeat a string n times:
(0..n).map(|_| s).collect::<String>(). It becomes slightly more
complicated to do it “right” (sizing the allocation up front), which
warrants a method that does it for us.

This method is useful in writing testcases, or when generating text.
format!() can be used to repeat single characters, but not repeating
strings like this.

[rust-highfive]

r? @aturon

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[bluss]

This method is called .rep(n: usize) -> String in crate odds, so it has been tested & used from there. It was also mentioned in this issue rust-lang/rfcs/issues/1253.

[frewsxcv]

Compile errors

error: use of unstable library feature 'repeat_str' (see issue #0)
    --> src/libcollections/../libcollectionstest/str.rs:1291:19
     |
1291 |     assert_eq!("".repeat(3), "");
     |                   ^^^^^^
     |
     = help: add #![feature(repeat_str)] to the crate attributes to enable

error: use of unstable library feature 'repeat_str' (see issue #0)
    --> src/libcollections/../libcollectionstest/str.rs:1292:22
     |
1292 |     assert_eq!("abc".repeat(0), "");
     |                      ^^^^^^
     |
     = help: add #![feature(repeat_str)] to the crate attributes to enable

error: use of unstable library feature 'repeat_str' (see issue #0)
    --> src/libcollections/../libcollectionstest/str.rs:1293:20
     |
1293 |     assert_eq!("α".repeat(3), "ααα");
     |                    ^^^^^^
     |
     = help: add #![feature(repeat_str)] to the crate attributes to enable

error: aborting due to 3 previous errors

Build failed, waiting for other jobs to finish...
error: Could not compile `collections`.

[bluss]

Thanks. Fixed by amending. Yes I'm letting the bots do the compiling for me.

[pmarcelll]

I have an interesting idea, would it make sense to add a collect_into method to iterators? It could take a mutable reference to a container, so the buffer can be preallocated. I know that it would require something different than FromIterator, so it should probably be on the Rust 2.0 wishlist, but I think it still make sense to add something like this.

[bluss]

@pmarcelll That sounds just like the existing String::extend(&mut self, iterable).

[pmarcelll]

Oh, I knew about extend, but I didn't know it's completely generic. This is awesome!

[alexcrichton]

Looks reasonable to me! I'd also be fine extending iterators/collections with more methods like this, but in isolation str::repeat seems like a fine method to have.

cc @rust-lang/libs

[alexcrichton]

Let's see if this works...

@rfcbot disposition merge

Only thing I see missing is a tracking issue, but we can fill that in when it's agreed to land.

[alexcrichton]

@rfcbot fcp merge

[rfcbot]

FCP proposed with disposition to merge. Review requested from:

• @BurntSushi
• @Kimundi
• @alexcrichton
• @aturon
• @brson
• @sfackler

No concerns currently listed.
See this document for info about what commands tagged team members can give me.

[aturon]

I'm fine with this convenience (though I feel like we explicitly cut away some things like this on the road to 1.0).

[rfcbot]

All relevant subteam members have reviewed. No concerns remain.

[bluss]

Amended the commit to point to tracking issue #37079

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 2b7222d has been approved by alexcrichton

[bluss]

@bors rollup

[rfcbot]

It has been one week since all blocks to the FCP were resolved.