[Proposal]Make .map return the calling collection type

Yogev_Sitton · April 12, 2016, 8:55am

Map is great for transforming an array of objects - it is very useful and I use it a lot.
I would love to use Map with Dictionaries and other collections as well.

As an example - let’s say I have a dictionary [String : Person] - that maps a person to an ID.
I want to use the map function a get a [String : String] - a dictionary that maps a person’s name to an ID.
Currently - the map method is defined to always return an array so that is not possible to do.

Obviously there are a lot of ways to accomplish the same task - but it would be very nice to be able to use map for other types than Array.

gribozavr · April 12, 2016, 9:02am

Hi,

We can discuss adding special-case functions to individual collections
where it makes sense, but it does not make sense to do it for
collections in general, please see

github.com

apple/swift/blob/main/docs/StdlibRationales.rst#high-order-functions-on-collections-return-arrays

:orphan:

=================================================
Rationales for the Swift standard library designs
=================================================

This document collects rationales for the Swift standard library.  It is not
meant to document all possible designs that we considered, but might describe
some of those, when important to explain the design that was chosen.

Current designs
===============

Some ``NSString`` APIs are mirrored on ``String``
-------------------------------------------------

There was not enough time in Swift 1.0 to design a rich ``String`` API, so we
reimplemented most of ``NSString`` APIs on ``String`` for parity.  This brought
the exact ``NSString`` semantics of those APIs, for example, treatment of
Unicode or behavior in edge cases (for example, empty strings), which we might

This file has been truncated. show original

for the rationale.

Dmitri

···

On Tue, Apr 12, 2016 at 1:55 AM, Yogev Sitton via swift-evolution <swift-evolution@swift.org> wrote:

Map is great for transforming an array of objects - it is very useful and I use it a lot.
I would love to use Map with Dictionaries and other collections as well.

As an example - let’s say I have a dictionary [String : Person] - that maps a person to an ID.
I want to use the map function a get a [String : String] - a dictionary that maps a person’s name to an ID.
Currently - the map method is defined to always return an array so that is not possible to do.

--
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr@gmail.com>*/