```ruby
class AddCrossPlatformToActivity < ActiveRecord::Migration[5.2]
  def change
    add_column :activities, :cross_platform, :boolean, default: true
  end
end
```

Fix default value of cross_platform
user
```ruby
class AddCrossPlatformToActivity < ActiveRecord::Migration[5.2]
  def change
    add_column :activities, :cross_platform, :boolean, default: false
  end
end
```
assistant