Ruby rubocop: how to freeze an array constant gene

问题:

I'm assigning an array constant like this:

NUMS = *(2..9)

Rubocop says

C: Freeze mutable objects assigned to constants.
NUMS = *(2..9)
               ^^^^^

---

So I try

NUMS = *(2..9).freeze

Rubocop says

C: Freeze mutable objects assigned to constants.
NUMS = *(2..9).freeze
               ^^^^^^^^^^^^

---

Tried

NUMS = (*(2..9)).freeze

Rubocop says

E: unexpected token tRPAREN (Using Ruby 2.0 parser; configure using TargetRubyVersion parameter, under AllCops)
NUMS = (*(2..9)).freeze
                         ^

---

Tried

NUMS = [1, 2, 3, 4, 5, 6, 7, 8, 9].freeze

Rubocop says

== happy_robot_dance (no errors)

I say

My hand hurts from typing 1, 2, 3, ... 9

Is there some way to use the splat to assign and freeze a constant?

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Solutions

NUMS = (2..9).to_a.freeze

NUMS = Array(2..9).freeze

回答1:

This case was previously unaccounted for by RuboCop (read bug.)

I have added an issue and a pull request that will fix this.

Meanwhile you can silence the cop by disabling it for this case using:

# rubocop:disable Style/MutableConstant
NUMS = *(2..9)
# rubocop:enable Style/MutableConstant

Or you can use #to_a:

NUMS = (2..9).to_a.freeze

回答2:

I think this is a case of appeasing Rubocop for its own sake - case 2 looks like it should work and therefore could be considered a bug. However, does this work?

why_do_i_exist = *(2..9)
NUMS = why_do_i_exist.freeze

回答3:

You can try:

NUMS = Array[*2..9].freeze