warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
warning: The called method `test' is defined here

Ruby 2.7 deprecated the use of hashes in the last argument of a method call. Luckily, this can be resolved by removing the curly braces of a direct hash argument, or adding a hash splat ** to a variable argument

For these examples, we’ll be using the following sample function to demonstrate the warnings:

def hello(name: 'World')
  "Hello, #{name}!"
end

Plain Hash Argument

When a hash is the last argument in a method and the method expects keyword arguments, then Ruby automatically converts this argument into keyword arguments.

Solution

To remove the warning, we can simply remove the curly braces. This solution works for any number of keywords.

Variable Hash Argument

Likewise, when a hash is passed as a variable in the final argument slot, it is also converted into keyword arguments. Since this hash could be coming from elsewhere in the application, it isn’t always as easy as moving the hash into the method parameters and removing curly braces…

details = { name: 'Alex' }
hello(details)

Solution

Luckily, Ruby has a feature called a “hash splat” (**). When a hash splat is applied on a hash, it expands the hash’s keys into multiple arguments, allowing this error to be dissipated as the method receives keyword arguments rather than receiving a hash.

details = { name: 'Alex' }
hello(**details)

Suppress Warning without Fix (Not Recommended)

If we want to suppress this warning, we can do this via an environment variable.

Solution: Export Environment Variable

After executing export RUBYOPT='-W:no-deprecated', any Ruby command will ignore deprecation notices. This sets an environment variable telling Ruby to ignore deprecation notices.

If instead, you want to ignore notices per command, you must use the inline environment variable syntax, RUBYOPT='-W:no-deprecated' ruby file.rb.

For instance, for a Rails app, you would use RUBYOPT='-W:no-deprecated' rails server

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