Use defined?(yield) and SIZED_ENUMERATOR

array.rb

@@ -44,7 +44,7 @@ class Array
   def each
     Primitive.attr! :inline_block
     unless defined?(yield)
-      return to_enum(:each) { self.length }
+      return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, ary_enum_length)'
     end
     _i = 0
     value = nil

kernel.rb

@@ -129,7 +129,7 @@ def tap
   #
   def then
     Primitive.attr! :inline_block
-    unless block_given?
+    unless defined?(yield)
       return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_obj_size)'
     end
     yield(self)
@@ -145,7 +145,7 @@ def then
   #
   def yield_self
     Primitive.attr! :inline_block
-    unless block_given?
+    unless defined?(yield)
       return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_obj_size)'
     end
     yield(self)
@@ -182,8 +182,8 @@ def yield_self
   #    } #=> :ok
   def loop
     Primitive.attr! :inline_block
-    unless block_given?
-      return enum_for(:loop) { Float::INFINITY }
+    unless defined?(yield)
+      return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, rb_f_loop_size)'
     end
 
     begin

numeric.c

@@ -5664,6 +5664,12 @@ int_downto(VALUE from, VALUE to)
     return from;
 }
 
+static VALUE
+int_dotimes_size(VALUE num, VALUE args, VALUE eobj)
+{
+    return int_neg_p(num) ? INT2FIX(0) : num;
+}
+
 /*
  *  call-seq:
  *    round(ndigits= 0, half: :up) -> integer

numeric.rb

@@ -230,8 +230,8 @@ def size
   # With no block given, returns an Enumerator.
   def times
     Primitive.attr! :inline_block
-    unless block_given?
-      return to_enum(:times) { self < 0 ? 0 : self }
+    unless defined?(yield)
+      return Primitive.cexpr! 'SIZED_ENUMERATOR(self, 0, 0, int_dotimes_size)'
     end
     i = 0
     while i < self

object.c

@@ -3988,6 +3988,12 @@ f_sprintf(int c, const VALUE *v, VALUE _)
     return rb_f_sprintf(c, v);
 }
 
+static VALUE
+rb_f_loop_size(VALUE self, VALUE args, VALUE eobj)
+{
+    return DBL2NUM(HUGE_VAL);
+}
+
 /*
  *  Document-class: Class
  *