make Range::size() constexpr

[folly.git] / folly / Range.h

diff --git a/folly/Range.h b/folly/Range.h
index 4913aef403580330a3609e474ff315791913273e..4a06491684549db077af179fb49270e4223375f8 100644 (file)
--- a/folly/Range.h
+++ b/folly/Range.h
@@ -17,8 +17,7 @@
 // @author Mark Rabkin (mrabkin@fb.com)
 // @author Andrei Alexandrescu (andrei.alexandrescu@fb.com)
 
-#ifndef FOLLY_RANGE_H_
-#define FOLLY_RANGE_H_
+#pragma once
 
 #include <folly/FBString.h>
 #include <folly/Portability.h>
@@ -354,8 +353,13 @@ public:
     reset(str.data(), str.size());
   }
 
-  size_type size() const {
-    assert(b_ <= e_);
+  constexpr size_type size() const {
+    // It would be nice to assert(b_ <= e_) here.  This can be achieved even
+    // in a C++11 compatible constexpr function:
+    // http://ericniebler.com/2014/09/27/assert-and-constexpr-in-cxx11/
+    // Unfortunately current gcc versions have a bug causing it to reject
+    // this check in a constexpr function:
+    // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71448
     return e_ - b_;
   }
   size_type walk_size() const {
@@ -1147,5 +1151,3 @@ struct hasher<folly::Range<T*>,
 #pragma GCC diagnostic pop
 
 FOLLY_ASSUME_FBVECTOR_COMPATIBLE_1(folly::Range);
-
-#endif // FOLLY_RANGE_H_