Reimplements Range#first

Range#first shouldn't call `Range#to_a` on infinity range.

1 files changed, 31 insertions, 0 deletions

diff --git a/mrbgems/mruby-range-ext/mrblib/range.rb b/mrbgems/mruby-range-ext/mrblib/range.rb
new file mode 100644
index 000000000..3b9c3874a
--- /dev/null
+++ b/mrbgems/mruby-range-ext/mrblib/range.rb
@@ -0,0 +1,31 @@
+class Range
+  ##
+  # call-seq:
+  #    rng.first    -> obj
+  #    rng.first(n) -> an_array
+  #
+  # Returns the first object in the range, or an array of the first +n+
+  # elements.
+  #
+  #   (10..20).first     #=> 10
+  #   (10..20).first(3)  #=> [10, 11, 12]
+  #
+  def first(*args)
+    return self.begin if args.empty?
+
+    raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 1)" unless args.length == 1
+    nv = args[0]
+    raise TypeError, "no implicit conversion from nil to integer" unless nv.nil?.!
+    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless nv.respond_to?(:to_int)
+    n = nv.to_int
+    raise TypeError, "no implicit conversion of #{nv.class} into Integer" unless n.kind_of?(Integer)
+    raise ArgumentError, "negative array size (or size too big)" unless 0 <= n
+    ary = []
+    each do |i|
+      break if n <= 0
+      ary.push(i)
+      n -= 1
+    end
+    ary
+  end
+end