From 6567e3b13eb7d6fc2fa4ff7593c06bb4dccdb6c9 Mon Sep 17 00:00:00 2001
From: Caspian Baska <email@caspian.computer>
Date: Mon, 24 Oct 2022 22:58:36 +0800
Subject: [PATCH] Add `Enumerable(T)#to_set(& : T -> U) : Set(U) forall U`

---
 spec/std/enumerable_spec.cr | 14 ++++++++++++++
 src/set.cr                  | 10 ++++++++++
 2 files changed, 24 insertions(+)

diff --git a/spec/std/enumerable_spec.cr b/spec/std/enumerable_spec.cr
index 2bcc7d92ccb3..f75389f2f1a8 100644
--- a/spec/std/enumerable_spec.cr
+++ b/spec/std/enumerable_spec.cr
@@ -130,6 +130,20 @@ describe "Enumerable" do
     end
   end
 
+  describe "#to_set" do
+    context "without block" do
+      it "creates a Set from the unique elements of the collection" do
+        {1, 1, 2, 3}.to_set.should eq Set{1, 2, 3}
+      end
+    end
+
+    context "with block" do
+      it "creates a Set from running the block against the collection's elements" do
+        {1, 2, 3, 4, 5}.to_set { |i| i // 2 }.should eq Set{0, 1, 2}
+      end
+    end
+  end
+
   describe "chunk" do
     it "works" do
       [1].chunk { true }.to_a.should eq [{true, [1]}]
diff --git a/src/set.cr b/src/set.cr
index 2d70a8bde059..40ccd12f4653 100644
--- a/src/set.cr
+++ b/src/set.cr
@@ -486,4 +486,14 @@ module Enumerable
   def to_set : Set(T)
     Set.new(self)
   end
+
+  # Returns a new `Set` with the unique results of running *block* against each
+  # element of the enumerable.
+  def to_set(&block : T -> U) : Set(U) forall U
+    set = Set(U).new
+    each do |elem|
+      set << yield elem
+    end
+    set
+  end
 end