Note that hidden friending could have negative modularity effects. Do you really want std::complex to need to pull in iosfwd first before hidden friending op<< ? This would also mean that the module that has std::complex has to pull in the module that has iostreams.

From: Lib-Ext <lib-ext-bounces_at_[hidden]> On Behalf Of Corentin via Lib-Ext
Sent: Monday, March 9, 2020 3:12 PM
To: Evolution Working Group mailing list <ext_at_[hidden]>
Cc: Corentin <corentin.jabot_at_[hidden]>; modules_at_lists.isocpp.org; C++ Library Evolution Working Group <lib-ext_at_[hidden]>; ISO C++ Tooling Study Group <sg15_at_[hidden]>; Billy O'Neal (VC LIBS) <bion_at_[hidden]>
Subject: [EXTERNAL] Re: [isocpp-lib-ext] [isocpp-ext] [SG15] Modularization of the standard library andABI stability



On Mon, 9 Mar 2020 at 21:08, Billy O'Neal (VC LIBS) via Ext <ext_at_[hidden]<mailto:ext_at_[hidden]>> wrote:
Most of those overload set effects appear unintentional and we should look at "hidden friend"-ing all of them.

+1

________________________________
From: Ext <ext-bounces_at_[hidden]<mailto:ext-bounces_at_[hidden]>> on behalf of JeanHeyd Meneide via Ext <ext_at_[hidden]<mailto:ext_at_[hidden]>>
Sent: Monday, March 9, 2020 12:55 PM
To: Evolution Working Group mailing list <ext_at_[hidden]<mailto:ext_at_[hidden]>>; modules_at_[hidden]<mailto:modules_at_[hidden]> <modules_at_[hidden]<mailto:modules_at_[hidden]>>; ISO C++ Tooling Study Group <sg15_at_[hidden]<mailto:sg15_at_[hidden]>>; C++ Library Evolution Working Group <lib-ext_at_[hidden]<mailto:lib-ext_at_[hidden]>>
Cc: JeanHeyd Meneide <phdofthehouse_at_[hidden]<mailto:phdofthehouse_at_[hidden]>>
Subject: Re: [isocpp-ext] [SG15] Modularization of the standard library andABI stability

Dear Tooling/EWG/LEWG,

On Mon, Mar 9, 2020 at 3:36 PM Steve Downey via Ext
<ext_at_[hidden]<mailto:ext_at_[hidden]>> wrote:
>
> In particular, I'd like to see, and measure, the costs of having large overload sets present before committing to a module the size of `std` as opposed to smaller ones where I can exclude parts I am uninterested in.
>

     I echo Steve's concern here. "import std;" can possibly lead to a
lot of suboptimal overload resolution. For example, clang-format
accidentally brought in extra overload sets related to std::locale and
tanked someone's performance just because of the order of includes:
https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Ftravisdowns.github.io%2Fblog%2F2019%2F11%2F19%2Ftoupper.html&amp;data=02%7C01%7Cbion%40microsoft.com%7C4516b16941c64e934cc708d7c463cc0a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637193805220385630&amp;sdata=vi2SJdjeiTYX0kx3CNadLbuhHyWstxIVn8rATyXfW4Y%3D&amp;reserved=0<https://urldefense.com/v3/__https:/nam06.safelinks.protection.outlook.com/?url=https*3A*2F*2Ftravisdowns.github.io*2Fblog*2F2019*2F11*2F19*2Ftoupper.html&amp;data=02*7C01*7Cbion*40microsoft.com*7C4516b16941c64e934cc708d7c463cc0a*7C72f988bf86f141af91ab2d7cd011db47*7C1*7C0*7C637193805220385630&amp;sdata=vi2SJdjeiTYX0kx3CNadLbuhHyWstxIVn8rATyXfW4Y*3D&amp;reserved=0__;JSUlJSUlJSUlJSUlJSUlJSU!!FbZ0ZwI3Qg!4cToOe-ahsjUyy7hdj_ATGUOQXT4L_6cjKyfkfkPY9NSdj8SXL5lPGtOt_IU$>

     C++ is incredibly sensitive to what entities are available. Since
we do not have a selection syntax (e.g., import std with { vector,
string, find_if, ... }), then our only way to control visibility --
and thus, overload resolution -- is with carefully crafted module
buckets. While there is probably no harm in having "import std;" exist
in general, we should be mindful of the problems that already exist
with "expose all the functions and types, ever" for existing and new
code. Therefore, I think both "import std;" as well as more targeted
library buckets should be considered.

Sincerely,
JeanHeyd
_______________________________________________
Ext mailing list
Ext_at_[hidden]<mailto:Ext_at_[hidden]>
Subscription: https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.isocpp.org%2Fmailman%2Flistinfo.cgi%2Fext&amp;data=02%7C01%7Cbion%40microsoft.com%7C4516b16941c64e934cc708d7c463cc0a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637193805220385630&amp;sdata=gCqfTZuDmKbEJj08Iq%2FJDQq9rEcgpvjOCXQ%2BNTLd9LI%3D&amp;reserved=0<https://urldefense.com/v3/__https:/nam06.safelinks.protection.outlook.com/?url=https*3A*2F*2Flists.isocpp.org*2Fmailman*2Flistinfo.cgi*2Fext&amp;data=02*7C01*7Cbion*40microsoft.com*7C4516b16941c64e934cc708d7c463cc0a*7C72f988bf86f141af91ab2d7cd011db47*7C1*7C0*7C637193805220385630&amp;sdata=gCqfTZuDmKbEJj08Iq*2FJDQq9rEcgpvjOCXQ*2BNTLd9LI*3D&amp;reserved=0__;JSUlJSUlJSUlJSUlJSUlJSU!!FbZ0ZwI3Qg!4cToOe-ahsjUyy7hdj_ATGUOQXT4L_6cjKyfkfkPY9NSdj8SXL5lPOGdmVlF$>
Link to this post: https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Flists.isocpp.org%2Fext%2F2020%2F03%2F12970.php&amp;data=02%7C01%7Cbion%40microsoft.com%7C4516b16941c64e934cc708d7c463cc0a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637193805220385630&amp;sdata=oGZkMKrYm3I2dzXq5%2B5G8QoWSb7q1GcgfnEiOofVJLs%3D&amp;reserved=0<https://urldefense.com/v3/__https:/nam06.safelinks.protection.outlook.com/?url=http*3A*2F*2Flists.isocpp.org*2Fext*2F2020*2F03*2F12970.php&amp;data=02*7C01*7Cbion*40microsoft.com*7C4516b16941c64e934cc708d7c463cc0a*7C72f988bf86f141af91ab2d7cd011db47*7C1*7C0*7C637193805220385630&amp;sdata=oGZkMKrYm3I2dzXq5*2B5G8QoWSb7q1GcgfnEiOofVJLs*3D&amp;reserved=0__;JSUlJSUlJSUlJSUlJSUlJSU!!FbZ0ZwI3Qg!4cToOe-ahsjUyy7hdj_ATGUOQXT4L_6cjKyfkfkPY9NSdj8SXL5lPNoKW9ev$>
_______________________________________________
Ext mailing list
Ext_at_[hidden]<mailto:Ext_at_[hidden].org>
Subscription: https://lists.isocpp.org/mailman/listinfo.cgi/ext<https://urldefense.com/v3/__https:/lists.isocpp.org/mailman/listinfo.cgi/ext__;!!FbZ0ZwI3Qg!4cToOe-ahsjUyy7hdj_ATGUOQXT4L_6cjKyfkfkPY9NSdj8SXL5lPFqioVDs$>
Link to this post: http://lists.isocpp.org/ext/2020/03/12971.php<https://urldefense.com/v3/__http:/lists.isocpp.org/ext/2020/03/12971.php__;!!FbZ0ZwI3Qg!4cToOe-ahsjUyy7hdj_ATGUOQXT4L_6cjKyfkfkPY9NSdj8SXL5lPM2z7SgF$>