Avoid allocations in Ability class.

[huacnlee]

It won't change anything after they are first invoke, so add method cache to avoid allocations and avoid GC.

Benchmarks:

Calculating -------------------------------------
project_guest_rules without method cache
                        79.352k i/100ms
project_guest_rules with method cache
                        93.634k i/100ms
-------------------------------------------------
project_guest_rules without method cache
                          2.865M (±32.5%) i/s -     11.982M
project_guest_rules with method cache
                          4.419M (± 7.4%) i/s -     22.004M

Comparison:
project_guest_rules with method cache:  4418908.0 i/s
project_guest_rules without method cache:  2864514.0 i/s - 1.54x slower

Calculating -------------------------------------
project_report_rules without method cache
                        53.126k i/100ms
project_report_rules with method cache
                        97.473k i/100ms
-------------------------------------------------
project_report_rules without method cache
                          1.093M (±36.5%) i/s -      4.675M
project_report_rules with method cache
                          4.420M (± 7.2%) i/s -     22.029M
Comparison:
project_report_rules with method cache:  4420054.3 i/s
project_report_rules without method cache:  1092509.6 i/s - 4.05x slower

Benchark case:

https://gist.github.com/huacnlee/b04788ae6df42fe769e4

[Razer6]

Awesome. @yorickpeterse @randx Can you take a look?

[yorickpeterse]

Since all these methods return constant data, can we not just use a constant instead (and return said constant from the method)?

[huacnlee]

@yorickpeterse That no difference but it will make code little complex and hard to read, method cache is simple.

class Ability
  class << self
    PROJECT_GUEST_RULES = [
      :read_project,
      :read_wiki,
      :read_issue,
      :read_label,
      :read_milestone,
      :read_project_snippet,
      :read_project_member,
      :read_merge_request,
      :read_note,
      :read_build,
      :create_project,
      :create_issue,
      :create_note
    ]

    ...

    def project_guest_rules
      PROJECT_GUEST_RULES
    end
  end
end

VS

class Ability
  class << self
    def project_guest_rules
      @project_guest_rules ||= [
        :read_project,
        :read_wiki,
        :read_issue,
        :read_label,
        :read_milestone,
        :read_project_snippet,
        :read_project_member,
        :read_merge_request,
        :read_note,
        :read_build,
        :create_project,
        :create_issue,
        :create_note
      ]
    end
  end
end

[yorickpeterse]

Fair enough, I don't see any problems with using instance variables instead.

[dzaporozhets]

Looks good. We will merge it a bit later (after 8.3.0.rc2)

[huacnlee]

@randx You looks like forgot this PR, version 8.3.0 have released

[dzaporozhets]

@huacnlee good reminder. Lets merge it

[huacnlee]

😄