Add Fiddle::MemoryView.available?

Fiddle had no binding for `rb_memory_view_available_p()`, which callers can use to check whether an object supports the memory view protocol.

Author: himura467

ext/fiddle/memory_view.c

@@ -96,6 +96,12 @@ rb_fiddle_memview_release(VALUE obj)
     return Qnil;
 }
 
+static VALUE
+rb_fiddle_memview_s_available_p(VALUE klass, VALUE target)
+{
+    return rb_memory_view_available_p(target) ? Qtrue : Qfalse;
+}
+
 static VALUE
 rb_fiddle_memview_s_export(VALUE klass, VALUE target)
 {
@@ -307,6 +313,7 @@ Init_fiddle_memory_view(void)
 {
     rb_cMemoryView = rb_define_class_under(mFiddle, "MemoryView", rb_cObject);
     rb_define_alloc_func(rb_cMemoryView, rb_fiddle_memview_s_allocate);
+    rb_define_singleton_method(rb_cMemoryView, "available?", rb_fiddle_memview_s_available_p, 1);
     rb_define_singleton_method(rb_cMemoryView, "export", rb_fiddle_memview_s_export, 1);
     rb_define_method(rb_cMemoryView, "initialize", rb_fiddle_memview_initialize, 1);
     rb_define_method(rb_cMemoryView, "release", rb_fiddle_memview_release, 0);

test/fiddle/test_memory_view.rb

@@ -30,6 +30,12 @@ def test_memory_view_from_unsupported_obj
       end
     end
 
+    def test_available?
+      assert_equal(true, MemoryView.available?(Pointer["hello world"]))
+      assert_equal(false, MemoryView.available?(Fiddle::NULL))
+      assert_equal(false, MemoryView.available?(Object.new))
+    end
+
     def test_memory_view_from_pointer
       str = Marshal.load(Marshal.dump("hello world"))
       ptr = Pointer[str]