# Rails 5.2
class User < ApplicationRecord
  validates :email, presence: true
end

> user = User.new
=> #<User id: nil, name: nil, email: nil, rating: 0, password: nil, created_at: nil, updated_at: nil>

> user.valid?
=> false

> user.errors
=> #<ActiveModel::Errors:0x00007fc46700df10 @base=#<User id: nil, name: nil, email: nil, rating: 0, password: nil, created_at: nil, updated_at: nil>, @messages={:email=>["can't be blank"], :password=>["can't be blank"]}, @details={:email=>[{:error=>:blank}], :password=>[{:error=>:blank}]}>

> user.errors.slice!
=> Traceback (most recent call last):
        1: from (irb):16
NoMethodError (undefined method 'slice!' for #<ActiveModel::Errors:0x00007fa1f0e46eb8>)
Did you mean?  slice_when

> errors = user.errors.to_h

> errors.slice!(:email)
=> {:password=>["can't be blank"]}

> errors
=> {:email=>["can't be blank"]}