Add Iterator::max_size_hint #57360

clarfonthey · 2019-01-05T23:12:40Z

This is an alternative to #48544 (since closed) which adds a max_size_hint method to Iterator. It should be merged after #56932, and the actual change is in commit 21348899c7c3068028d6c490edd3482f5e6392bb.

The idea of a "minimum size" is confusing for iterators and iterables, because it's unclear where this should exactly be described. However, the maximum size is unambiguous and will improve the upper bound hints for flatten and flat_map.

I figured that I'd create a PR here so that people can discuss the change, even though it probably won't be added immediately.

rust-highfive · 2019-01-05T23:12:51Z

r? @alexcrichton

(rust_highfive has picked a reviewer for you, use r? to override)

Centril · 2019-01-06T00:50:00Z

How does this square with boat's comment about object safety?
(i.e. will you be able to make Travis go green?)

scottmcm · 2019-01-09T01:45:00Z

I'm pretty sure the upper bounds are (sadly) completely unused: https://internals.rust-lang.org/t/is-size-hint-1-ever-used/8187?u=scottmcm

So I'm not sure how much good this will do in practice, much as I like it in theory.

clarfonthey · 2019-01-09T02:36:44Z

How does this square with boat's comment about object safety?
(i.e. will you be able to make Travis go green?)

You're right-- I've changed from a constant to a method instead. This limits its use in constants until some version of const Trait comes around, but it should do fine for all uses in size_hint.

rust-highfive · 2019-01-09T02:45:02Z

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:09b3d33c:start=1547001510636797919,finish=1547001580405810453,duration=69769012534
$ 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
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:03:25]    Compiling cc v1.0.25
[00:03:25]    Compiling libc v0.2.46
[00:03:25]    Compiling core v0.0.0 (/checkout/src/libcore)
[00:03:25]    Compiling unwind v0.0.0 (/checkout/src/libunwind)
[00:03:25] error: expected one of `,` or `}`, found `.`
[00:03:25]    --> src/libcore/iter/adapters/flatten.rs:236:18
[00:03:25]     |
[00:03:25] 236 |                 f.checked_add(b)?.checked_add(m.checked_mul(max)?)?
[00:03:25]     |                  ^ expected one of `,` or `}` here
[00:03:26]    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
[00:03:31] error[E0422]: cannot find struct, variant or union type `catch` in this scope
[00:03:31]    --> src/libcore/iter/adapters/flatten.rs:235:55
[00:03:31]     |
[00:03:31]     |
[00:03:31] 235 |             (Some(f), Some(b), Some(m), Some(max)) => catch {
[00:03:31] 
[00:03:31]    Compiling compiler_builtins v0.1.4
[00:03:31]    Compiling cmake v0.1.33
[00:03:31]    Compiling backtrace-sys v0.1.27
---
[00:03:36]    Compiling rustc_asan v0.0.0 (/checkout/src/librustc_asan)
[00:03:41] error[E0308]: mismatched types
[00:03:41]     --> src/libcore/option.rs:1178:43
[00:03:41]      |
[00:03:41] 1178 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:41]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:41]      |                           |
[00:03:41]      |                           expected `option::Option<usize>` because of return type
[00:03:41]      |
[00:03:41]      = note: expected type `option::Option<usize>`
[00:03:41] 
[00:03:41] error[E0308]: mismatched types
[00:03:41]     --> src/libcore/option.rs:1226:43
[00:03:41]      |
[00:03:41]      |
[00:03:41] 1226 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:41]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:41]      |                           |
[00:03:41]      |                           expected `option::Option<usize>` because of return type
[00:03:41]      |
[00:03:41]      = note: expected type `option::Option<usize>`
[00:03:41] 
[00:03:41] error[E0308]: mismatched types
[00:03:41]     --> src/libcore/option.rs:1265:43
[00:03:41]      |
[00:03:41]      |
[00:03:41] 1265 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:41]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:41]      |                           |
[00:03:41]      |                           expected `option::Option<usize>` because of return type
[00:03:41]      |
[00:03:41]      = note: expected type `option::Option<usize>`
[00:03:41] 
[00:03:42] error[E0308]: mismatched types
[00:03:42]     --> src/libcore/result.rs:1083:43
[00:03:42]      |
[00:03:42]      |
[00:03:42] 1083 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:42]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:42]      |                           |
[00:03:42]      |                           expected `option::Option<usize>` because of return type
[00:03:42]      |
[00:03:42]      = note: expected type `option::Option<usize>`
[00:03:42] 
[00:03:42] error[E0308]: mismatched types
[00:03:42]     --> src/libcore/result.rs:1130:43
[00:03:42]      |
[00:03:42]      |
[00:03:42] 1130 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:42]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:42]      |                           |
[00:03:42]      |                           expected `option::Option<usize>` because of return type
[00:03:42]      |
[00:03:42]      = note: expected type `option::Option<usize>`
[00:03:42] 
[00:03:42] error[E0308]: mismatched types
[00:03:42]     --> src/libcore/result.rs:1175:43
[00:03:42]      |
[00:03:42]      |
[00:03:42] 1175 |     fn max_size_hint() -> Option<usize> { 1 }
[00:03:42]      |                           -------------   ^ expected enum `option::Option`, found integral variable
[00:03:42]      |                           |
[00:03:42]      |                           expected `option::Option<usize>` because of return type
[00:03:42]      |
[00:03:42]      = note: expected type `option::Option<usize>`
[00:03:42] 
[00:03:44] error: aborting due to 8 previous errors
[00:03:44] 
[00:03:44] Some errors occurred: E0308, E0422.
---
[00:03:44] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:03:44] expected success, got: exit code: 101
[00:03:44] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:03:44] Build completed unsuccessfully in 0:00:21
[00:03:44] make: *** [all] Error 1
[00:03:44] Makefile:18: recipe for target 'all' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:07ab2fea
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Wed Jan  9 02:43:34 UTC 2019
---
travis_time:end:1a5b739e:start=1547001815085521184,finish=1547001815090210210,duration=4689026
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:11504506
$ 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:0180b712
travis_time:start:0180b712
$ 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:2a765984
$ 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)

bors · 2019-01-13T19:56:22Z

☔ The latest upstream changes (presumably #57577) made this pull request unmergeable. Please resolve the merge conflicts.

clarfonthey · 2019-01-15T22:00:56Z

Rebased. Is there something wrong with the current implementation of try right now? I thought that the issues wrt macro resolution were solved, but apparently not…

rust-highfive · 2019-01-15T22:06:09Z

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:08356510:start=1547589672919180181,finish=1547589675227109024,duration=2307928843
$ 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
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:04:18]    Compiling cc v1.0.28
[00:04:18]    Compiling libc v0.2.46
[00:04:18]    Compiling core v0.0.0 (/checkout/src/libcore)
[00:04:18]    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
[00:04:18] error: expected one of `,` or `}`, found `.`
[00:04:18]    --> src/libcore/iter/adapters/flatten.rs:236:18
[00:04:18]     |
[00:04:18] 236 |                 f.checked_add(b)?.checked_add(m.checked_mul(max)?)?
[00:04:18]     |                  ^ expected one of `,` or `}` here
[00:04:19]    Compiling unwind v0.0.0 (/checkout/src/libunwind)
[00:04:23] error[E0574]: expected struct, variant or union type, found macro `try`
[00:04:23]    --> src/libcore/iter/adapters/flatten.rs:235:55
[00:04:23]     |
[00:04:23]     |
[00:04:23] 235 |             (Some(f), Some(b), Some(m), Some(max)) => try {
[00:04:23]     |                                                       ^^^ did you mean `try!(...)`?
[00:04:24]    Compiling compiler_builtins v0.1.4
[00:04:24]    Compiling cmake v0.1.33
[00:04:24]    Compiling backtrace-sys v0.1.27
[00:04:26]    Compiling std v0.0.0 (/checkout/src/libstd)
---
[00:04:37] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:04:37] expected success, got: exit code: 101
[00:04:37] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:04:37] Build completed unsuccessfully in 0:00:20
[00:04:37] make: *** [all] Error 1
[00:04:37] Makefile:18: recipe for target 'all' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:301c870a
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Jan 15 22:06:03 UTC 2019

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)

bors · 2019-01-21T16:48:33Z

☔ The latest upstream changes (presumably #55045) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive · 2019-01-22T22:52:20Z

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:1db4d200:start=1548197257754658772,finish=1548197260104091967,duration=2349433195
$ 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
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:04:04]    Compiling cc v1.0.28
[00:04:04]    Compiling core v0.0.0 (/checkout/src/libcore)
[00:04:04]    Compiling libc v0.2.46
[00:04:04]    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
[00:04:05] error: expected one of `,` or `}`, found `.`
[00:04:05]    --> src/libcore/iter/adapters/flatten.rs:236:18
[00:04:05]     |
[00:04:05] 236 |                 f.checked_add(b)?.checked_add(m.checked_mul(max)?)?
[00:04:05]     |                  ^ expected one of `,` or `}` here
[00:04:06]    Compiling unwind v0.0.0 (/checkout/src/libunwind)
[00:04:10] error[E0574]: expected struct, variant or union type, found macro `try`
[00:04:10]    --> src/libcore/iter/adapters/flatten.rs:235:55
[00:04:10]     |
[00:04:10]     |
[00:04:10] 235 |             (Some(f), Some(b), Some(m), Some(max)) => try {
[00:04:10]     |                                                       ^^^ did you mean `try!(...)`?
[00:04:11]    Compiling compiler_builtins v0.1.4
[00:04:11]    Compiling cmake v0.1.33
[00:04:11]    Compiling backtrace-sys v0.1.27
[00:04:13]    Compiling std v0.0.0 (/checkout/src/libstd)
---
[00:04:24] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:04:24] expected success, got: exit code: 101
[00:04:24] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:04:24] Build completed unsuccessfully in 0:00:22
[00:04:24] make: *** [all] Error 1
[00:04:24] Makefile:18: recipe for target 'all' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:079fea58
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Tue Jan 22 22:52:15 UTC 2019

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)

rust-highfive · 2019-01-31T05:52:09Z

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:07c31680:start=1548913633872644963,finish=1548913636070937308,duration=2198292345
$ 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
Setting environment variables from .travis.yml
$ export IMAGE=x86_64-gnu-llvm-6.0
---
[00:04:19]    Compiling cc v1.0.28
[00:04:19]    Compiling libc v0.2.46
[00:04:19]    Compiling core v0.0.0 (/checkout/src/libcore)
[00:04:19]    Compiling unwind v0.0.0 (/checkout/src/libunwind)
[00:04:19] error: expected one of `,` or `}`, found `.`
[00:04:19]    --> src/libcore/iter/adapters/flatten.rs:236:18
[00:04:19]     |
[00:04:19] 236 |                 f.checked_add(b)?.checked_add(m.checked_mul(max)?)?
[00:04:19]     |                  ^ expected one of `,` or `}` here
[00:04:19]    Compiling build_helper v0.1.0 (/checkout/src/build_helper)
[00:04:24] error[E0574]: expected struct, variant or union type, found macro `try`
[00:04:24]    --> src/libcore/iter/adapters/flatten.rs:235:55
[00:04:24]     |
[00:04:24]     |
[00:04:24] 235 |             (Some(f), Some(b), Some(m), Some(max)) => try {
[00:04:24]     |                                                       ^^^ did you mean `try!(...)`?
[00:04:25]    Compiling compiler_builtins v0.1.5
[00:04:25]    Compiling cmake v0.1.33
[00:04:25]    Compiling backtrace-sys v0.1.27
[00:04:28]    Compiling std v0.0.0 (/checkout/src/libstd)
---
[00:04:37] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "build" "--target" "x86_64-unknown-linux-gnu" "-j" "4" "--release" "--locked" "--color" "always" "--features" "panic-unwind backtrace" "--manifest-path" "/checkout/src/libstd/Cargo.toml" "--message-format" "json"
[00:04:37] expected success, got: exit code: 101
[00:04:37] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap build
[00:04:37] Build completed unsuccessfully in 0:00:21
[00:04:37] make: *** [all] Error 1
[00:04:37] Makefile:18: recipe for target 'all' failed
The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:27fc9b7c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)
Thu Jan 31 05:52:04 UTC 2019
---
travis_time:end:03b3c9d4:start=1548913925852079980,finish=1548913925856721395,duration=4641415
travis_fold:end:after_failure.3
travis_fold:start:after_failure.4
travis_time:start:0cffa42e
$ 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:1067c9d6
travis_time:start:1067c9d6
$ 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:18762618
$ 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)

Dylan-DPC-zz · 2019-02-11T20:28:11Z

ping from triage @clarcharr @alexcrichton any updates on this?

alexcrichton · 2019-02-12T13:05:07Z

I wonder if this would perhaps be best moved to an internals thread or an issue? The description of this PR indicates it's largely here for discussion, but it doesn't seem to have a lot of discussion.

clarfonthey · 2019-02-12T23:57:47Z

Honestly? That's reasonable. I'm just going to close this for now because I don't really have the energy to start a discussion for the time being, although I'll revisit this at some point if no one else does.

rust-highfive assigned alexcrichton Jan 5, 2019

rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jan 5, 2019

clarfonthey force-pushed the max_size_hint branch from c8dc788 to c0d0a75 Compare January 5, 2019 23:16

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clarfonthey force-pushed the max_size_hint branch 2 times, most recently from a4d8e11 to 8132f5a Compare January 9, 2019 02:34

clarfonthey changed the title ~~Add Iterator::MAX_SIZE_HINT~~ Add Iterator::max_size_hint Jan 9, 2019

clarfonthey force-pushed the max_size_hint branch from 8132f5a to 3d1194c Compare January 9, 2019 02:37

clarfonthey force-pushed the max_size_hint branch 5 times, most recently from 43ea988 to bc01591 Compare January 10, 2019 14:04

clarfonthey force-pushed the max_size_hint branch from bc01591 to eb18ed3 Compare January 15, 2019 21:59

clarfonthey force-pushed the max_size_hint branch from eb18ed3 to b8cfa89 Compare January 22, 2019 22:46

Add Iterator::max_size_hint

200d71b

clarfonthey force-pushed the max_size_hint branch from b8cfa89 to 200d71b Compare January 31, 2019 05:45

clarfonthey closed this Feb 12, 2019

clarfonthey deleted the max_size_hint branch January 29, 2022 22:30

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Add Iterator::max_size_hint #57360

Add Iterator::max_size_hint #57360

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Add Iterator::max_size_hint #57360

Add Iterator::max_size_hint #57360

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alexcrichton commented Feb 12, 2019

clarfonthey commented Feb 12, 2019

clarfonthey commented Jan 5, 2019 •

edited

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Centril commented Jan 6, 2019 •

edited

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