Add Enumerable#to_h(&block)

spec/std/enumerable_spec.cr

@@ -872,5 +872,9 @@ describe "Enumerable" do
     it "for array" do
       [[:a, :b], [:c, :d]].to_h.should eq({:a => :b, :c => :d})
     end
+
+    it "with block" do
+      (1..3).to_h { |i| {i, i ** 2} }.should eq({1 => 1, 2 => 4, 3 => 9})
+    end
   end
 end

src/enumerable.cr

@@ -1291,4 +1291,17 @@ module Enumerable(T)
       hash[item[0]] = item[1]
     end
   end
+
+  # Creates a `Hash` out of an returned from a *block* Enumerable, where each
+  # element is a 2 element structure (for instance a `Tuple` or an `Array`).
+  #
+  # ```
+  # (1..3).to_h { |i| {i, i ** 2} } # => {1 => 1, 2 => 4, 3 => 9}
+  # ```
+  def to_h(&block : T -> Tuple(K, V)) forall K, V
+    each_with_object({} of K => V) do |item, hash|
+      item_pair = yield item
+      hash[item_pair[0]] = item_pair[1]
+    end
+  end
 end