Add CheckedNumeric::AssignIfValid() method

base/numerics/safe_math.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_MATH_H_
 #define BASE_NUMERICS_SAFE_MATH_H_
 
 #include <stddef.h>
 
 #include <limits>
@@ skipping 24 matching lines @@
 // The unary negation, increment, and decrement operators are supported, along
 // with the following unary arithmetic methods, which return a new
 // CheckedNumeric as a result of the operation:
 //  Abs() - Absolute value.
 //  UnsignedAbs() - Absolute value as an equival-width unsigned underlying type
 //          (valid for only integral types).
 //
 // The following methods convert from CheckedNumeric to standard numeric values:
 //  IsValid() - Returns true if the underlying numeric value is valid (i.e. has
 //          has not wrapped and is not the result of an invalid conversion).
+// AssignIfValid() - Assigns the underlying value to the supplied destination
+//          pointer if the value is currently valid and within the range

[scottmg, 2016/11/25 23:47:51]

indent

+//          supported by the destination type. Returns true on success.
 //  ValueOrDie() - Returns the underlying value. If the state is not valid this
 //          call will crash on a CHECK.
 //  ValueOrDefault() - Returns the current value, or the supplied default if the
 //          state is not valid (will not trigger a CHECK).
 //  ValueFloating() - Returns the underlying floating point value (valid only
 //          for floating point CheckedNumeric types; will not cause a CHECK).
 //
 // The following are general utility methods that are useful for converting
 // between arithmetic types and CheckedNumeric types:
 //  CheckedNumeric::Cast<Dst>() - Instance method returning a CheckedNumeric
@@ skipping 37 matching lines @@
                   "Argument must be numeric.");
   }
 
   // This is not an explicit constructor because we want a seamless conversion
   // from StrictNumeric types.
   template <typename Src>
   constexpr CheckedNumeric(
       StrictNumeric<Src> value)  // NOLINT(runtime/explicit)
       : state_(static_cast<Src>(value)) {}
 
-  // IsValid() is the public API to test if a CheckedNumeric is currently valid.
+  // IsValid() - The public API to test if a CheckedNumeric is currently valid.
   // A range checked destination type can be supplied using the Dst template
-  // parameter, which will trigger a CHECK if the value is not in bounds for
-  // the destination.
+  // parameter.
   template <typename Dst = T>
   constexpr bool IsValid() const {
     return state_.is_valid() &&
            IsValueInRangeForNumericType<Dst>(state_.value());
   }
 
-  // ValueOrDie() The primary accessor for the underlying value. If the current
-  // state is not valid it will CHECK and crash.
+  // AssignIfValid(Dst) - Assigns the underlying value if it is currently valid
+  // and is within the range supported by the destination type. Returns true if
+  // successful and false otherwise.
+  template <typename Dst>
+  constexpr bool AssignIfValid(Dst* result) const {
+    return IsValid<Dst>() ? ((*result = static_cast<Dst>(state_.value())), true)
+                          : false;
+  }
+
+  // ValueOrDie() - The primary accessor for the underlying value. If the
+  // current state is not valid it will CHECK and crash.
   // A range checked destination type can be supplied using the Dst template
   // parameter, which will trigger a CHECK if the value is not in bounds for
   // the destination.
   // The CHECK behavior can be overridden by supplying a handler as a
   // template parameter, for test code, etc. However, the handler cannot access
   // the underlying value, and it is not available through other means.
   template <typename Dst = T, class CheckHandler = CheckOnFailure>
   constexpr Dst ValueOrDie() const {
     return IsValid<Dst>() ? state_.value()
                           : CheckHandler::template HandleFailure<Dst>();
   }
 
-  // ValueOrDefault(T default_value) A convenience method that returns the
+  // ValueOrDefault(T default_value) - A convenience method that returns the
   // current value if the state is valid, and the supplied default_value for
   // any other state.
   // A range checked destination type can be supplied using the Dst template
   // parameter. WARNING: This function may fail to compile or CHECK at runtime
   // if the supplied default_value is not within range of the destination type.
   template <typename Dst = T, typename Src>
   constexpr Dst ValueOrDefault(const Src default_value) const {
     return IsValid<Dst>() ? state_.value() : checked_cast<Dst>(default_value);
   }
 
@@ skipping 255 matching lines @@
 using internal::CheckMod;
 using internal::CheckLsh;
 using internal::CheckRsh;
 using internal::CheckAnd;
 using internal::CheckOr;
 using internal::CheckXor;
 
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_MATH_H_