Make checked_cast a constexpr

base/numerics/safe_conversions.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_NUMERICS_SAFE_CONVERSIONS_H_
 #define BASE_NUMERICS_SAFE_CONVERSIONS_H_
 
 #include <stddef.h>
 
 #include <limits>
@@ skipping 23 matching lines @@
 }
 
 template <typename T>
 constexpr typename std::enable_if<!std::numeric_limits<T>::is_signed,
                                   bool>::type IsValueNegative(T) {
   static_assert(std::numeric_limits<T>::is_specialized,
                 "Argument must be numeric.");
   return false;
 }
 
-// checked_cast<> is analogous to static_cast<> for numeric types,
-// except that it CHECKs that the specified numeric conversion will not
-// overflow or underflow. NaN source will always trigger a CHECK.
-template <typename Dst, typename Src>
-inline Dst checked_cast(Src value) {
-  CHECK(IsValueInRangeForNumericType<Dst>(value));
-  return static_cast<Dst>(value);
-}
-
-// HandleNaN will cause this class to CHECK(false).
-struct SaturatedCastNaNBehaviorCheck {
+// Just fires a CHECK(false). Used for numeric boundary errors.
+struct CheckOnFailure {
   template <typename T>
-  static T HandleNaN() {
+  static T HandleFailure() {
     CHECK(false);
     return T();
   }
 };
 
+// checked_cast<> is analogous to static_cast<> for numeric types,
+// except that it CHECKs that the specified numeric conversion will not
+// overflow or underflow. NaN source will always trigger a CHECK.
+template <typename Dst,
+          class CheckHandler = CheckOnFailure,
+          typename Src>
+constexpr Dst checked_cast(Src value) {
+  // This throws a compile-time error on evaluating the constexpr if it can be
+  // determined at compile-time as failing, otherwise it will CHECK at runtime.
+  return IsValueInRangeForNumericType<Dst>(value)
+             ? static_cast<Dst>(value)
+             : CheckHandler::template HandleFailure<Dst>();
+}
+
 // HandleNaN will return 0 in this case.
 struct SaturatedCastNaNBehaviorReturnZero {
   template <typename T>
-  static constexpr T HandleNaN() {
+  static constexpr T HandleFailure() {
     return T();
   }
 };
 
 namespace internal {
 // This wrapper is used for C++11 constexpr support by avoiding the declaration
 // of local variables in the saturated_cast template function.
 template <typename Dst, class NaNHandler, typename Src>
 constexpr Dst saturated_cast_impl(const Src value,
                                   const RangeConstraint constraint) {
   return constraint == RANGE_VALID
              ? static_cast<Dst>(value)
              : (constraint == RANGE_UNDERFLOW
                     ? std::numeric_limits<Dst>::min()
                     : (constraint == RANGE_OVERFLOW
                            ? std::numeric_limits<Dst>::max()
                            : (constraint == RANGE_INVALID
-                                  ? NaNHandler::template HandleNaN<Dst>()
+                                  ? NaNHandler::template HandleFailure<Dst>()
                                   : (NOTREACHED(), static_cast<Dst>(value)))));
 }
 }  // namespace internal
 
 // saturated_cast<> is analogous to static_cast<> for numeric types, except
 // that the specified numeric conversion will saturate rather than overflow or
 // underflow. NaN assignment to an integral will defer the behavior to a
 // specified class. By default, it will return 0.
 template <typename Dst,
           class NaNHandler = SaturatedCastNaNBehaviorReturnZero,
@@ skipping 63 matching lines @@
  private:
   const T value_;
 };
 
 // Explicitly make a shorter size_t typedef for convenience.
 typedef StrictNumeric<size_t> SizeT;
 
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_CONVERSIONS_H_