• SimonN (22/22) Sep 02 2020 Hi,
• Steven Schveighoffer (9/24) Sep 02 2020 mutability attributes are not deducted for templates.
• SimonN (9/14) Sep 02 2020 Thanks! I've never looked much into template this -- at first

SimonN <eiderdaus gmail.com> writes:

Hi,

About this issue in Phobos:
https://issues.dlang.org/show_bug.cgi?id=21216
SortedRange.empty should be const, .front should be inout

Just adding const/inout to SortedRange's methods won't be enough; 
if we add const/inout here, then many other Phobos ranges need to 
become const/inout-correct to keep the tests passing. Before I 
dive deeper into annotating their methods, I would like to verify 
my assumptions on how template function attribute deduction works:

1) I know that templated functions deduce their own attributes on 
instantiation. But front()/empty() are non-templated methods 
within the templated struct SortedRange. Will attribute deduction 
happen here?

2) Is it sensible/possible to force attribute deduction by 
declaring empty() in SortedRange as a zero-argument template? 
I.e.:
      property bool empty()() { return this._input.empty; }

3) Should I rather annotate the non-templated 
SortedRange.empty/.front manually? But with what, then? empty() 
should probably be const, but it's never  nogc if annotated 
manually, even if the wrapped range offers empty()  nogc.

-- Simon

Steven Schveighoffer <schveiguy gmail.com> writes:

On 9/2/20 5:23 PM, SimonN wrote:
 Hi,
 
 About this issue in Phobos:
 https://issues.dlang.org/show_bug.cgi?id=21216
 SortedRange.empty should be const, .front should be inout
 
 Just adding const/inout to SortedRange's methods won't be enough; if we 
 add const/inout here, then many other Phobos ranges need to become 
 const/inout-correct to keep the tests passing. Before I dive deeper into 
 annotating their methods, I would like to verify my assumptions on how 
 template function attribute deduction works:
 
 1) I know that templated functions deduce their own attributes on 
 instantiation. But front()/empty() are non-templated methods within the 
 templated struct SortedRange. Will attribute deduction happen here?

mutability attributes are not deducted for templates.

wrapping ranges such as SortedRange can't really specify const or inout 
on their methods via introspection of the underlying range. What they 
can do is template the `this` parameter. Then if the underlying range 
supports calling that way, it will work, otherwise it won't.

using `template this` should be compatible with the existing code I 
would think.

-Steve

SimonN <eiderdaus gmail.com> writes:

On Wednesday, 2 September 2020 at 21:40:59 UTC, Steven 
Schveighoffer wrote:
 What they can do is template the `this` parameter. Then if the 
 underlying range supports calling that way, it will work, 
 otherwise it won't.

 using `template this` should be compatible with the existing 
 code I would think.

Thanks! I've never looked much into template this -- at first 
glance, it offers what inout already offers -- but it sounds like 
the right tool for the job. (inout would straightaway disallow 
calls to mutable methods.)

https://dlang.org/spec/template.html#template_this_parameter

I'll experiment with it!

-- Simon