Demo FromIterator short-circuiting

[pnkfelix]

while looking at a FIXME in FromIterator for Option and FromIterator for Result, I realized that the current documentation does not have example code showing exactly what is meant by "no further elements are taken."

The code snippets provided here are meant to correct that.

[rust-highfive]

r? @dtolnay

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[Centril]

Looks great, thanks!

r? @Centril @bors r+ rollup

[bors]

📌 Commit d5a61c0 has been approved by Centril

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

travis_time:end:1dfc8b41:start=1553255332022655938,finish=1553255412763729794,duration=80741073856
$ git checkout -qf FETCH_HEAD
travis_fold:end:git.checkout

Encrypted environment variables have been removed for security reasons.
See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
$ export SCCACHE_BUCKET=rust-lang-ci-sccache2
$ export SCCACHE_REGION=us-west-1
$ export GCP_CACHE_BUCKET=rust-lang-ci-cache
Setting environment variables from .travis.yml
---
travis_time:start:test_assembly
Check compiletest suite=assembly mode=assembly (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:25:07] 
[01:25:07] running 9 tests
[01:25:07] iiiiiiiii
[01:25:07] 
[01:25:07]  finished in 0.156
[01:25:07] travis_fold:end:test_assembly

---
travis_time:start:test_debuginfo
Check compiletest suite=debuginfo mode=debuginfo-both (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:25:23] 
[01:25:23] running 120 tests
[01:25:49] .iiiii...i.....i..i...i..i.i...i.ii...i.....i..i....i..........iiii..........i...ii...i.......ii.i.i 100/120
[01:25:54] .i......iii.i.....ii
[01:25:54] 
[01:25:54]  finished in 30.859
[01:25:54] travis_fold:end:test_debuginfo

---
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[01:42:40] 
[01:42:40] failures:
[01:42:40] 
[01:42:40] 
[01:42:40] ---- option.rs - option::Option<V>::from_iter (line 1321) stdout ----
[01:42:40] error: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an operator, found `;`
[01:42:40]   --> option.rs:1328:25
[01:42:40]    |
[01:42:40] 10 |     .map(|x| shared += x; x.checked_sub(2))
[01:42:40]    |                         ^ expected one of 8 possible tokens here
[01:42:40] error[E0425]: cannot find value `x` in this scope
[01:42:40]   --> option.rs:1328:27
[01:42:40]    |
[01:42:40]    |
[01:42:40] 10 |     .map(|x| shared += x; x.checked_sub(2))
[01:42:40]    |                           ^ not found in this scope
[01:42:40] error[E0061]: this function takes 1 parameter but 2 parameters were supplied
[01:42:40]   --> option.rs:1328:6
[01:42:40]    |
[01:42:40]    |
[01:42:40] 10 |     .map(|x| shared += x; x.checked_sub(2))
[01:42:40] 
[01:42:40] error: aborting due to 3 previous errors
[01:42:40] 
[01:42:40] Some errors occurred: E0061, E0425.
[01:42:40] Some errors occurred: E0061, E0425.
[01:42:40] For more information about an error, try `rustc --explain E0061`.
[01:42:40] thread 'option.rs - option::Option<V>::from_iter (line 1321)' panicked at 'couldn't compile the test', src/librustdoc/test.rs:310:13
[01:42:40] note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
[01:42:40] 
[01:42:40] ---- result.rs - result::Result<V, E>::from_iter (line 1220) stdout ----
[01:42:40] error: expected one of `!`, `)`, `,`, `.`, `::`, `?`, `{`, or an operator, found `;`
[01:42:40]   |
[01:42:40] 7 |     shared += x;
[01:42:40]   |                ^ expected one of 8 possible tokens here
[01:42:40] 
[01:42:40] 
[01:42:40] error[E0425]: cannot find value `x` in this scope
[01:42:40]  --> result.rs:1225:5
[01:42:40]   |
[01:42:40] 8 |     x.checked_sub(2).ok_or("Underflow!")
[01:42:40]   |     ^ help: a local variable with a similar name exists: `v`
[01:42:40] error[E0061]: this function takes 1 parameter but 2 parameters were supplied
[01:42:40]  --> result.rs:1223:52
[01:42:40]   |
[01:42:40]   |
[01:42:40] 6 | let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
[01:42:40] 
[01:42:40] error: aborting due to 3 previous errors
[01:42:40] 
[01:42:40] Some errors occurred: E0061, E0425.
---
[01:42:40] 
[01:42:40] error: test failed, to rerun pass '--doc'
[01:42:40] 
[01:42:40] 
[01:42:40] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "-p" "core" "--" "--quiet"
[01:42:40] 
[01:42:40] 
[01:42:40] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[01:42:40] Build completed unsuccessfully in 0:29:33
[01:42:40] Build completed unsuccessfully in 0:29:33
[01:42:40] make: *** [check] Error 1
[01:42:40] Makefile:48: recipe for target 'check' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:08c35b2c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Fri Mar 22 13:33:01 UTC 2019
---
travis_time:end:19fe9dfe:start=1553261583421882948,finish=1553261583427197903,duration=5314955
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:129e781a
$ ln -s . checkout && for CORE in obj/cores/core.*; do EXE=$(echo $CORE | sed 's|obj/cores/core\.[0-9]*\.!checkout!\(.*\)|\1|;y|!|/|'); if [ -f "$EXE" ]; then printf travis_fold":start:crashlog\n\033[31;1m%s\033[0m\n" "$CORE"; gdb --batch -q -c "$CORE" "$EXE" -iex 'set auto-load off' -iex 'dir src/' -iex 'set sysroot .' -ex bt -ex q; echo travis_fold":"end:crashlog; fi; done || true
travis_fold:end:after_failure.4
travis_fold:start:after_failure.5
travis_time:start:06060120
travis_time:start:06060120
$ cat ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers || true
cat: ./obj/build/x86_64-unknown-linux-gnu/native/asan/build/lib/asan/clang_rt.asan-dynamic-i386.vers: No such file or directory
travis_fold:end:after_failure.5
travis_fold:start:after_failure.6
travis_time:start:113dd558
$ dmesg | grep -i kill

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[Centril]

@bors r-

(r=me with @killercup's fix / green travis)

[DevQps]

Just as a question from a relative newbie: What is this 3_u16 syntax? I have seen the 3u16 syntax but never with the underscore. Is there a difference between this syntax?

I would suggest that using 3u16 or even let items: Vec<u16>= vec![3, 2, 1, 10]; to make it more clear for people that are not too experienced with Rust. But that is just my humble opinion!

EDIT: Nice examples by the way! I never knew it worked this way :)

[Centril]

The _ here is merely an effect of separators in numeric literals, e.g. 3_000_000_u32 or 3_000____u32. The underscores are for readability and have no effect otherwise. 3u16 and 3_u16 are thus equivalent.

[DevQps]

Alright! Thanks for sharing! :)

[Centril]

@bors r+ rollup

[bors]

📌 Commit 0e83e96 has been approved by Centril