Add Indexable#index! overloads with offset parameter (#12089)

spec/std/indexable_spec.cr

@@ -93,6 +93,28 @@ describe Indexable do
     end
   end
 
+  describe "#index!" do
+    it "offset type" do
+      indexable = SafeIndexable.new(3)
+      indexable.index!(1, 0_i64).should eq 1
+      indexable.index!(1, 0_i64).should be_a(Int64)
+    end
+
+    it "raises if no element is found" do
+      indexable = SafeIndexable.new(3)
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(0, -100) }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(0, -4) }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(0, 1) }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(0, 3) }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(0, 100) }
+
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(-4) { true } }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(3) { true } }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(2) { false } }
+      expect_raises(Enumerable::NotFoundError) { indexable.index!(-3) { false } }
+    end
+  end
+
   describe "#rindex" do
     it "does rindex with big negative offset" do
       indexable = SafeIndexable.new(3)

src/indexable.cr

@@ -742,8 +742,8 @@ module Indexable(T)
     hasher
   end
 
-  # Returns the index of the first appearance of *value* in `self`
-  # starting from the given *offset*, or `nil` if the value is not in `self`.
+  # Returns the index of the first appearance of *object* in `self`
+  # starting from the given *offset*, or `nil` if *object* is not in `self`.
   #
   # ```
   # [1, 2, 3, 1, 2, 3].index(2, offset: 2) # => 4
@@ -771,6 +771,28 @@ module Indexable(T)
     nil
   end
 
+  # Returns the index of the first appearance of *obj* in `self`
+  # starting from the given *offset*. Raises `Enumerable::NotFoundError` if
+  # *obj* is not in `self`.
+  #
+  # ```
+  # [1, 2, 3, 1, 2, 3].index!(2, offset: 2) # => 4
+  # ```
+  def index!(obj, offset : Int = 0)
+    index(obj, offset) || raise Enumerable::NotFoundError.new
+  end
+
+  # Returns the index of the first object in `self` for which the block
+  # is truthy, starting from the given *offset*. Raises
+  # `Enumerable::NotFoundError` if no match is found.
+  #
+  # ```
+  # [1, 2, 3, 1, 2, 3].index!(offset: 2) { |x| x < 2 } # => 3
+  # ```
+  def index!(offset : Int = 0, & : T ->)
+    index(offset) { |e| yield e } || raise Enumerable::NotFoundError.new
+  end
+
   # Returns the last element of `self` if it's not empty, or raises `IndexError`.
   #
   # ```