h = Hash.new(10)
x = val unless x
It seems you've misunderstood what happens under the hood when using
augmented assignment with tables as '||=' then becomes syntactic sugar
for 'x[] = x[] || some_other_value' and the assignment is performed
via '[]=' rather than '='. '[]=' will not create a key if it believes
it already exists and this is the cause of the behaviour you're seeing.
h = Hash.new(10)
p h["blue"] => 10
h["blue"] ||= 20
p h => {}
In this case when '||=' invokes the assignment it finds that h["blue"]
already contains a value because of the default so the hash method
'[]=' doesn't attempt to create a new key because it appears that the
key already exists.
Contrast this to:
h = Hash.new(10)
p h["blue"] => 10
h["blue"] = nil
p h => { "blue" => nil }
h["blue"] ||= 10
p h => { "blue" => 10 }
h["blue"] ||= 20
p h => { "blue" => 10 }
Here the key has been explicitly set equal to nil and '||=' acts the
way we'd expect an augmented assignment to work with scalar types.
Finally if no default is set for the table:
h = {}
h["red"] ||= 10
p h => {"red" => 10}
The key is always created as expected.
