Avoid duplicated calls in StackableValue#[]

[brucehsu]

Fixing the performance issue mentioned in issue #1560 by eliminating duplicated calls of StackableValue#[] in one-liner conditionals.

[coveralls]

Coverage remained the same at 99.071% when pulling 061cf11 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into 3b91395 on ruby-grape:master.

[coveralls]

Coverage remained the same at 99.071% when pulling 061cf11 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into 3b91395 on ruby-grape:master.

[coveralls]

Coverage remained the same at 99.071% when pulling 061cf11 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into 3b91395 on ruby-grape:master.

[coveralls]

Coverage remained the same at 99.071% when pulling 061cf11 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into 3b91395 on ruby-grape:master.

[brucehsu]

Travis-CI builds are failing on Ruby 2.3.3 and Ruby 2.4, due to this issue in Rainbow 2.2.1 : ku1ik/rainbow#48

[brucehsu]

Please also refer to: travis-ci/travis-ci#7204

[brucehsu]

Fixed in PR #1562 .

[dblock]

This makes a lot of sense. Rebase (I merged #1562) please, and add a CHANGELOG line in line with something like "Improved performance of ..." so that it becomes a visible change.

[grape-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

Generated by 🚫 danger

[coveralls]

Coverage remained the same at 99.071% when pulling 882eb65 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into b4858f3 on ruby-grape:master.

[coveralls]

Coverage remained the same at 99.071% when pulling 882eb65 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into b4858f3 on ruby-grape:master.

[coveralls]

Coverage remained the same at 99.071% when pulling 882eb65 on brucehsu:feature/fix_excessive_recursion_in_stackablevalue into b4858f3 on ruby-grape:master.

[dblock]

Thanks @brucehsu. I'll make a minor release sometime soon.