[llvm] r185851 - [ADT/NullablePtr] Allow implicit conversion of NullablePtr<OtherT> -> NullablePtr<T> if OtherT is derived from T.

[Argyrios Kyrtzidis]

On Jul 8, 2013, at 5:31 PM, David Blaikie <dblaikie at gmail.com> wrote:

> On Mon, Jul 8, 2013 at 5:08 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com> wrote:
>> On Jul 8, 2013, at 4:05 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> 
>> On Mon, Jul 8, 2013 at 2:51 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com>
>> wrote:
>> 
>> On Jul 8, 2013, at 12:47 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> 
>> On Mon, Jul 8, 2013 at 12:12 PM, Argyrios Kyrtzidis <akyrtzi at gmail.com>
>> wrote:
>> 
>> Author: akirtzidis
>> Date: Mon Jul  8 14:12:01 2013
>> New Revision: 185851
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=185851&view=rev
>> Log:
>> [ADT/NullablePtr] Allow implicit conversion of NullablePtr<OtherT> ->
>> NullablePtr<T> if OtherT is derived from T.
>> 
>> 
>> Might be nicer to do this for any case where SrcT* is implicitly
>> convertible DestT* (such as adding cv qualifiers or converting to
>> void*).
>> 
>> 
>> cv qualifiers look like are working, void* is not.
>> In general, we need to add the equivalent of C++11's is_convertible to
>> "llvm/Support/type_traits.h" and use it here.
>> 
>> 
>> Shall we do that then?
>> 
>> (your current implementation also disables this ctor for NullablePtr's
>> of non-class type (NullablePtr<int> for example), I think... that
>> seems unreasonable)
>> 
>> 
>> Feel free to enhance it :-)
> 
> Alternatively, this code doesn't seem to have any uses inside the llvm
> codebase (at least not clang, llvm, compiler-rt, libcxx - maybe in
> lldb?) nor any tests. Should we just remove it instead? (I assume you
> have a use-case, or you wouldn't've been motivated to update it - is
> that use case somewhere in the llvm project (broadly, across all
> subprojects) or out of tree?)

It is used out of tree.

> 
> - David
> 
>> 
>> -Argyrios
>> 
>> 
>> 
>> 
>> 
>> Modified:
>>  llvm/trunk/include/llvm/ADT/NullablePtr.h
>> 
>> Modified: llvm/trunk/include/llvm/ADT/NullablePtr.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/NullablePtr.h?rev=185851&r1=185850&r2=185851&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/ADT/NullablePtr.h (original)
>> +++ llvm/trunk/include/llvm/ADT/NullablePtr.h Mon Jul  8 14:12:01 2013
>> @@ -14,6 +14,7 @@
>> #ifndef LLVM_ADT_NULLABLEPTR_H
>> #define LLVM_ADT_NULLABLEPTR_H
>> 
>> +#include "llvm/Support/type_traits.h"
>> #include <cassert>
>> #include <cstddef>
>> 
>> @@ -25,8 +26,17 @@ namespace llvm {
>> template<class T>
>> class NullablePtr {
>> T *Ptr;
>> +  struct PlaceHolder {};
>> +
>> public:
>> NullablePtr(T *P = 0) : Ptr(P) {}
>> +
>> +  template<typename OtherT>
>> +  NullablePtr(NullablePtr<OtherT> Other,
>> +              typename enable_if<
>> +                is_base_of<T, OtherT>,
>> +                PlaceHolder
>> +              >::type = PlaceHolder()) : Ptr(Other.getPtrOrNull()) {}
>> 
>> bool isNull() const { return Ptr == 0; }
>> bool isNonNull() const { return Ptr != 0; }
>> 
>> 
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