在Ruby / Rails中使用全局变量或常量变量？

Question

Say we have a connection to memcache or redis... which style is preferred and why?

MEMCACHE = Memcache.new(...)
REDIS = Redis.new(...)

OR

$memcache = Memcache.new(...)
$redis = Redis.new(...)

Answer 1

You might want to use Redis.current More info here

For example, in an initializer:

Redis.current = Redis.new(host: 'localhost', port: 6379)

And then in your other classes:

def stars
  redis.smembers("stars")
end

private

def redis
  Redis.current
end

Answer 2

They are not equivalent constructs. Depending on your application, they may or may not be interchangeable, but they are semantically different.

# MEMCACHE is a constant, subject to scoping constraints.
MEMCACHE = Memcache.new(...)

# $memcache is a global variable: declare it anywhere; use it anywhere.
$memcache = Memcache.new(...)

Answer 3

IMO a "constant", because it communicates that it's supposed to be... constant.

Globals don't imply they shouldn't be mutated.