Optimize C++ API

[zhaoyao73]

Pass parameter with reference instead of value.
Add const as well as it is not changed.

Description

Optimize some functions to pass reference instead of value. This could avoid unnecessary construction/destruction and copy.

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• tiny changes
• did a successful build
• For user-facing API changes, API doc string has been updated.
  Didn't find the API doc in mxnet.io/doxygen
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

Comments

I am not sure I could run a sanity test with it or how to run a unit test/sanity test against the change. But pass value -> pass reference, should be transparent to C++, although not like C's pass value->pass pointer.

[vandanavk]

@mxnet-label-bot add [C++, pr-awaiting-review]

@leleamol for review

[sandeep-krishnamurthy]

LGTM.
@leleamol

[zhaoyao73]

any idea why centos-cpu still not done?
Is it the only thing need to be done?

[zhaoyao73]

@marcoabreu May I ask why the centos-cpu still not done?

[marcoabreu]

Seems like it hasn't been kicked off. Please rebase to start another build

[larroy]

LGTM

[lebeg]

LGTM

[zhaoyao73]

do I need to do anything?

[larroy]

@marcoabreu are we missing statuses from github? Check centos-cpu

[marcoabreu]

@zhaoyao73 I have kicked off a build on your behalf. Sorry for the inconveniences.

[zhaoyao73]

@marcoabreu just a dummy question, can I start a CI build?

[marcoabreu]

Yeah, just make a new commit and it will automatically start a build

[larroy]

@mxnet-label-bot [pr-awaiting-merge]

[zhaoyao73]

weird, look at this PR it is still pr-awaiting-review, although I see @larrroy put the pr-awaiting-merge?

[marcoabreu]

You received two binding approvals, no requested changes and there are no outstanding discussions, thus the PR is ready to be merged.