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Dict is a hash-like type for crystal-lang. It uses binary search for lookups and insertion to ensure that the entries are always sorted. This means its performance on either of those operations will often be slightly worse than Hash(K,V). That being said, insertion of a scrambled array of 100,000 Int32 takes only half a second on my local machine, so it's still not too bad - I guess you just can't make crystal slow. However, inserting a scrambled array of 1,000,000 Int32 took nearly 85 seconds for Dict but took only half a second for Hash, so there is almost certainly some opportunity for optimization there - maybe you can make crystal slow after all. Lookups on the same data set was almost the same for both.

Where Dict(W,D) comes out ahead is with huge data sets, where repeated enumeration of a sorted list of elements is necessary. Since the effort of sorting the elements is frontloaded to the time of insertion, there is no need to ever manually sort the dictionary. In fact, Dict(W,D) doesn't even have a #sort method - it's a given!

In my testing of dict vs hash, I found that, compared to sorting a Hash's keys, Dict being pre-sorted usually more than makes up for the performance penalty paid during insertion, just on the first pass.

All in all, Dict(W,D)'s use case is probably niche at best, but it was a fun exercise to see if a key-value container type that might compete with Hash(K,V)'s performance could be built easily.


  1. Add the dependency to your shard.yml:

        github: galvertez/dict.cr
  2. Run shards install


require "dict.cr"

Dict(W,D) is meant to be used more or less like Hash(K,V).

dict = Dict{
  "something" => "nothing",
  "alpha" => "beta",
  "eleven" => 11,
  "seven thousand" => 7000

alpha = dict["alpha"] # => "beta"

For example, a script like

dict.each do |word, definition|
  printf "#{word} = #{definition}\n"

will print

alpha = beta
eleven = 11
seven thousand = 7000
something = nothing

If you like, you can use the english syntax, rather than [] and []=

dict.define "alpha", "beta"
dict.lookup "alpha" # => "beta"

As it currently stands, Dict(W,D) will likely not work properly with union types as the word (W), but should work just fine with union type definitions (D), because of how heavily it relies on Comparable(T)


  1. Fork it (https://github.com/galvertez/dict.cr/fork)
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request


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MIT License