The clamped gem allows to filter values by a provided whitelist. For example, "apple".clamped(%w[apple banana]) # "apple". If apple is not part of the array, nil is returned. This is e.g. useful to filter values provided by user input.

Ruby already supports clamping numbers:

10.clamp(12, 20) # 12

The clamped gem extends this to strings, symbols, arrays and hashes.

For example:

"apple".clamped(%w[banana orange]) # nil

"apple".clamped(%w[apple banana]) # "apple"

This is mostly useful when whitelisting user input:

ROLES = ["admin", "user"]

# assume params[:role] == "superadmin"

params[:role].clamped(ROLES, default: "guest") # "guest"

Install with gem install clamped or put gem "clamped" in your Gemfile. More information on https://github.com/metikular/clamped