I also don't like the NS_TRY name, it seems too close to MOZ_TRY. I would
prefer to avoid names which are identical except s/NS/MOZ/.
Perhaps NSRESULT_TRY would be a better name? It makes it clear that it is
performing the try against the nsresult type.
On Mon, May 8, 2017 at 10:17 AM, Ehsan Akhgari <ehsan.akhg...@gmail.com>
wrote:
> I think these seem like valuable additions to nscore.h. It would be
> helpful to extend these facilities that would allow more code to use the
> Result-based programming model.
>
> (I'm not too much of a fan of the NS_TRY name, but can't think of a better
> name myself... :/ )
>
>
>
> On 05/07/2017 03:34 PM, Kris Maglione wrote:
>
>> I've been trying to write most of my new code to use Result.h as much as
>> possible. When I have to mix Result-based code with nsresult-based code,
>> though, things tend to get ugly, and I wind up writing helpers. At this
>> point I've wound up writing the same helpers in 3 or 4 different places, so
>> it may be time to try to standardize on something.
>>
>> The helpers I've been using look something like:
>>
>> template <>
>> class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult>
>> {
>> nsresult mErrorValue;
>>
>> template<typename V, typename E2> friend class Result;
>>
>> public:
>> explicit GenericErrorResult(nsresult aErrorValue) :
>> mErrorValue(aErrorValue) {}
>>
>> operator nsresult() { return mErrorValue; }
>> };
>>
>> static inline Result<Ok, nsresult>
>> WrapNSResult(PRStatus aRv)
>> {
>> if (aRv != PR_SUCCESS) {
>> return Err(NS_ERROR_FAILURE);
>> }
>> return Ok();
>> }
>>
>> static inline Result<Ok, nsresult>
>> WrapNSResult(nsresult aRv)
>> {
>> if (NS_FAILED(aRv)) {
>> return Err(aRv);
>> }
>> return Ok();
>> }
>>
>> #define NS_TRY(expr) MOZ_TRY(WrapNSResult(expr))
>>
>> And their use looks something like:
>>
>> Result<nsCOMPtr<nsIFile>, nsresult>
>> GetFile(nsIFile* aBase, const char* aChild)
>> {
>> nsCOMPtr<nsIFile> file;
>> NS_TRY(aBase->Clone(getter_AddRefs(file)));
>> NS_TRY(aBase->AppendNative(aChild));
>>
>> return Move(file);
>> }
>>
>> nsresult
>> ReadFile(const char* aPath)
>> {
>> nsCOMPtr<nsIFile> file;
>> MOZ_TRY_VAR(file, GetFile(mBase, aPath));
>>
>> PRFileDesc* fd;
>> NS_TRY(file->OpenNSPRFileDesc(PR_RDONLY, 0, &fd));
>>
>> ...
>> return NS_OK;
>> }
>>
>> Where NS_TRY converts a nsresult or PRStatus to an appropriate Result or
>> GenericErrorResult, and the GenericErrorResult<nsresult> specialization
>> automatically converts an nsresult when used in nsresult-based code.
>>
>> Does this seem like the kind of thing we should implement in some
>> standard header, or would a different approach be better?
>>
>> -Kris
>> _______________________________________________
>> dev-platform mailing list
>> dev-platform@lists.mozilla.org
>> https://lists.mozilla.org/listinfo/dev-platform
>>
>
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