[swift-evolution] Adding Result to the Standard Library

Matthew Johnson matthew at anandabits.com
Thu Nov 2 14:20:24 CDT 2017

I have been writing code in a style that uses explicit effect handling lately.  In this style of code, a request describing an async task is returned from a function and later interpreted by a library.  When the task completes the library passes the result to completion handler that is part of the task description (which produces subsequent effects to interpret).  

It isn’t possible to express the completion handlers attached to task descriptions as an async call.  The function needs to return the task description immediately.  For this reason, I believe it will be necessary to continue using a Result type in code written in this style even after async / await is introduced.

> On Nov 2, 2017, at 1:53 PM, Dan Stenmark via swift-evolution <swift-evolution at swift.org> wrote:
> With the upcoming async-await constructs supporting do-try-catch natively, what would the use-case for an explicit Result type be?
> Dan
>> On Nov 2, 2017, at 11:08 AM, Jon Shier via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Swift-Evolution:
>> 	I’ve written a first draft of a proposal to add Result<T> to the standard library by directly porting the Result<T> type used in Alamofire to the standard library. I’d be happy to implement it (type and tests for free!) if someone could point me to the right place to do so. I’m not including it directly in this email, since it includes the full implementation and is therefore quite long. (Discourse, please!) 
>> https://github.com/jshier/swift-evolution/blob/master/proposals/0187-add-result-to-the-standard-library.md <https://github.com/jshier/swift-evolution/blob/master/proposals/0187-add-result-to-the-standard-library.md>
>> Thanks, 
>> Jon Shier
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