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### 2030. `packaged_task::result_type` should be removed

Section: 32.9.10 [futures.task] Status: C++11 Submitter: Anthony Williams Opened: 2010-11-12 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

`packaged_task::operator()` always returns `void`, regardless of the return type of the wrapped task. However, `packaged_task::result_type` is a typedef to the return type of the wrapped task. This is inconsistent with other uses of `result_type` in the standard, where it matches the return type of `operator()` (e.g. `function`, `owner_less`). This is confusing.

It also violates the TR1 `result_of` protocol, and thus makes `packaged_task` harder to use with anything that respects that protocol.

Finally, it is of little use anyway.

`packaged_task::result_type` should therefore be removed.

[2011-02-24 Reflector discussion]

Moved to Tentatively Ready after 5 votes.

Proposed resolution:

Alter the class definition of `packaged_task` in 32.9.10 [futures.task] p. 2 as follows:

>     template<class R, class... ArgTypes>
>     class packaged_task<R(ArgTypes...)> {
>     public:
>       typedef R result_type;
>       [...]
>     };