[llvm] r202609 - [C++11] Add support for OwningPtr<T> to be converted to and from

[Duncan P. N. Exon Smith]

On 2014 Mar 2, at 01:51, Ahmed Charles <acharles at outlook.com> wrote:

> __============================================================================== 
>> 
>> --- llvm/trunk/include/llvm/ADT/OwningPtr.h (original) 
>> +++ llvm/trunk/include/llvm/ADT/OwningPtr.h Sat Mar  1 21:38:32 2014 
>> @@ -17,6 +17,7 @@ 
>>  #include "llvm/Support/Compiler.h" 
>>  #include <cassert> 
>>  #include <cstddef> 
>> +#include <memory> 
>> 
>>  namespace llvm { 
>> 
>> @@ -39,6 +40,17 @@ public: 
>>      return *this; 
>>    } 
>> 
>> +  OwningPtr(std::unique_ptr<T> &&Other) : Ptr(Other.release()) {} 
>> + 
>> +  OwningPtr &operator=(std::unique_ptr<T> &&Other) { 
>> 
>> Why an rvalue reference to a unique_ptr rather than passing the  
>> unique_ptr by value? 
> 
> No particular reason, though I suppose it is one less write to memory if the optimizer can't remove it. I just didn't consider passing by value. Feel free to change, I don't have commit access yet.

An rvalue-reference makes sense here.  It makes it clear that OwningPtr
is taking ownership from unique_ptr.  In particular, its signature lines
up with the standard signature for move assignment operators:

   T &T::operator=(T &&);

Matching the signature makes it obvious that it’s the same semantic
operation.  (It’s also more efficient before compiler optimizations.)