Change the backing data structure of VarSet from slice to map

[ian-howell]

This will speed up most operations performed on a large set of Vars

More detailed information in this issue.

[k8s-ci-robot]

Welcome @ian-howell!

It looks like this is your first PR to kubernetes-sigs/kustomize 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-sigs/kustomize has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: ian-howell
To complete the pull request process, please assign monopole
You can assign the PR to them by writing /assign @monopole in a comment when ready.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ian-howell]

/assign @monopole Performance optimizations

[k8s-ci-robot]

@ian-howell: GitHub didn't allow me to assign the following users: Performance, optimizations.

Note that only kubernetes-sigs members and repo collaborators can be assigned and that issues/PRs can only have 10 assignees at the same time.
For more information please see the contributor guide

In response to this:

/assign @monopole Performance optimizations

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ian-howell]

I believe travis has croaked on this one. Closing and reopening to trigger a new build

[monopole]

so, this is a sorted list, not a map, because it optimizes for easily emitting a sorted list of var names in debugging and error messages. anyone who's builds are noticeably slowed by O(N) var lookups during a build is doing some use case that needs a blog post. How many vars would it take to make a noticeable difference? 10,000? Why would someone use that many?

don't mind the code change as long as String() emits a sorted list of var names.

[monopole]

Please toss in a String() method that calls this method so we get deterministic ordering when debugging.

[monopole]

/lgtm

[monopole]

nevermind, if it becomes an issue, will add the String()
thanks!