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Ruby default arguments article: use UNDEFINED instead of NO_VALUE like Rubinius does

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Holger Just 2017-01-02 19:32:23 +01:00
parent 5ef09ade7c
commit 494a6fd885
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10
source/articles/2016/detecting-default-arguments-in-ruby.html.md
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@ -89,16 +89,16 @@ with_flag('foo', 'value')
Another option is to use a different special default value which we have determined to never represent a valid value. Again, this is only required if we can not come up with a "normal" default value like `nil`, `0` or an empty array or hash.
In our example, we define a constant called `NO_VALUE` with an empty Object instance and use it as a default value. Since the object is not equal to any other value, you can use it as a special flag to determine that no value was passed and just compare the argument to the same `NO_VALUE` object.
In our example, we define a constant called `UNDEFINED` with an empty Object instance and use it as a default value. Since the object is not equal to any other value, you can use it as a special flag to determine that no value was passed and just compare the argument to the same `UNDEFINED` object.
```ruby
NO_VALUE = Object.new
UNDEFINED = Object.new
# => #<Object:0x007fd87284af38>
def with_value(required, optional = NO_VALUE)
def with_value(required, optional = UNDEFINED)
puts "required: #{required}"
if optional == NO_VALUE
if optional.equal?(UNDEFINED)
puts "no optional given: #{optional}"
else
puts "optional: #{optional}"
@ -106,7 +106,7 @@ def with_value(required, optional = NO_VALUE)
end
```
When calling the method, the comparisons work as expected. As you can see, the default value is initialized with the `NO_VALUE` constant when not passing the optional argument and thus is considered to be omitted.
When calling the method, the comparisons work as expected. As you can see, the default value is initialized with the `UNDEFINED` constant when not passing the optional argument and thus is considered to be omitted.
```ruby
with_value('bar')