ruby - 在 Ruby 中检测重复键的惯用方法？

Question

我刚刚注意到，如果您向散列提供重复的键，Ruby 不会引发异常，甚至不会发出警告:

$VERBOSE = true
key_value_pairs_with_duplicates = [[1,"a"], [1, "b"]]
# No warning produced
Hash[key_value_pairs_with_duplicates] # => {1=>"b"}
# Also no warning
hash_created_by_literal_with_duplicate_keys = {1 => "a", 1=> "b"} # => {1=>"b"}

对于key_value_pairs_with_duplicates，我可以检测重复键

keys = key_value_pairs_with_duplicates.map(&:first)
raise "Duplicate keys" unless keys.uniq == keys

或者通过做

procedurally_produced_hash = {}
key_value_pairs_with_duplicates.each do |key, value|
  raise "Duplicate key" if procedurally_produced_hash.has_key?(key)
  procedurally_produced_hash[key] = value
end

或者

hash = Hash[key_value_pairs_with_duplicates]
raise "Duplicate keys" unless hash.length == key_value_pairs_with_duplicates.length

但是有没有一种惯用的方法呢？

Answer 1

Hash#merge 采用可选 block 来定义如何处理重复键。

http://www.ruby-doc.org/core-1.9.3/Hash.html#method-i-merge

利用此 block 仅在重复键上调用这一事实:

>> a = {a: 1, b: 2}
=> {:a=>1, :b=>2}

>> a.merge(c: 3) { |key, old, new| fail "Duplicate key: #{key}" }
=> {:a=>1, :b=>2, :c=>3}

>> a.merge(b: 10, c: 3) { |key, old, new| fail "Duplicate key: #{key}" }
RuntimeError: Duplicate key: b