• d-bugmail puremagic.com (32/32) Mar 20 2022 https://issues.dlang.org/show_bug.cgi?id=22907

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=22907

          Issue ID: 22907
           Summary: Can't use core.lifetime.forward on inout parameter
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: druntime
          Assignee: nobody puremagic.com
          Reporter: snarwin+bugzilla gmail.com

As of DMD 2.099.0, the following program fails to compile:

---
inout(int)[] fun(inout(int)[] a)
{
    import core.lifetime: forward;
    return forward!a;
}
---

The error message is:

---
/dlang/dmd/linux/bin64/../../src/druntime/import/core/lifetime.d(1558): Error:
`inout` on `return` means `inout` must be on a parameter as well for `pure
nothrow  nogc  property  safe inout(int)[]()`
onlineapp.d(4): Error: template instance `onlineapp.fun.forward!(a)` error
instantiating
---

This happens because using core.lifetime.forward on a non-ref parameter creates
a zero-argument nested function that returns the parameter by value.

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