You can use a pair of empty braces to initialise a hash. But, if you try to access a non-existant key, Ruby returns nil
by default.
my_hash = {}
=> {}
my_hash[:foo]
=> nil
Sometimes it might be useful to set a default value. This could be anything: an empty string, a null object, an error…
Here, I've set a string as default.
my_hash = {}
=> {}
my_hash.default = "Not set"
=> "Not set"
my_hash[:foo]
=> "Not set"
my_hash[:bar]
=> "Not set"
Now, instead of getting nil
for a non-existant entry, I get the default value.
The hash remains empty because I have not created any entries.
my_hash
=> {}
Hash.new
accepts a proc which you can use to set default values.
my_hash = Hash.new { |_hash, key| "Value for #{key} not set!" }
=> {}
my_hash[:foo]
=> "Value for foo not set!"
my_hash[:bar]
=> "Value for bar not set!"
You can also tell the proc to create a new entry if one isn't found.
my_hash = Hash.new { |hash, key| hash[key] = "Not set" }
=> {}
my_hash[:foo]
=> "Not set"
my_hash[:bar]
=> "Not set"
my_hash
=> {:foo=>"Not set", :bar=>"Not set"}
See the ruby docs for more info.
Top comments (0)