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digitalmars.D.bugs - [Issue 23352] New: `in` and `out` foreach variables


          Issue ID: 23352
           Summary: `in` and `out` foreach variables
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: qs.il.paperinik gmail.com

In Herb Sutter’s proposal for a brand new C++ syntax¹, I found this gem:
 “In this proposal, for(in auto x : rng) automatically
 is both efficient and guaranteed to be read-only.”
This is something D could do, too. Our `foreach` loops can be foreach ( element; range) // copy foreach ( ref element; range) // reference² foreach (auto ref element; range) // copy/reference, depending on value category foreach ( in element; range) // see next paragraph foreach ( out element; range) // see next paragraph `in` and `out` elements have the same binding as `in` and `out` function parameters. They bind to opApply(int delegate(in Type)); and opApply(int delegate(out Type)); respectively. ¹ https://raw.githubusercontent.com/hsutter/708/main/708.pdf ² That `ref` is effectively `auto ref` is a known bug. --
Sep 21 2022