ruby on rails - What is the reason to use ||= instead of = in model to define a constant -


found in current project:

class video < activerecord::base   ...   valid_video_hosts ||= %w(www.youtube.com youtube.com vimeo.com www.vimeo.com)   ... end

usually use simple valid_video_hosts = %w(...) , haven't guess why previous developers used ||=

anybody know benefits?

update

i know ||= in general cases, question defining constant way in model.

||= used cheap way memoize value, other posters mention. however...

why memoize constant?

the author protecting against warnings when loading source file multiple times. (warning: initialized constant valid_video_hosts)


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