It's possible to create a Hash with duplicate keys using missing key block and update method

[robdavid]

Consider the following code

result = Hash(String,Int32).new{ |h,k| h[k] = 0 }
result.update("NAME") { |v| v+1 }
pp! result

Running this under Crystal 1.9.2 gives the expected result of:

result # => {"NAME" => 1}

However, from Crystal 1.10.1 up to 1.11.2 (latest) I'm seeing:

result # => {"NAME" => 0, "NAME" => 1}

with two values for the same key!

Also,

pp! result.size
pp! result["NAME"]

Gives

result.size # => 2
result["NAME"] # => 0

You can see this easily in the crystal playground

[HertzDevil]

Regression of #13590

[MatthewMerrill]

It is also possible using Hash#put_if_absent. IMHO, in addition to #14417 the private method insert_new should be removed in favor of upsert in put_if_absent.

my_hash = Hash(String, Int32).new
my_hash.put_if_absent("a") { |k| my_hash[k] = 1 }
p! my_hash
# my_hash # => {"a" => 1, "a" => 1}