[Issue 17763] [scope][DIP1000] The compiler treats implicit and explicit static array slicing differently

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17763

Walter Bright  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |INVALID

--- Comment #3 from Walter Bright  ---
(In reply to ZombineDev from comment #0)
> The problem is that the compiler disallows explicitly slicing a static array
> and passing the slice to a scope parameter, while if you rely on the
> implicit slicing it works without a problem.

Let's examine:

> use(c);// OK - this compiles.

The address of c is implicitly taken by its coercion to the parameter type of
Context[]. But this is allowed because the parameter is 'scope', and it cannot
escape.


> use(c[]);  // NG - doesn't compile, though should be
>// equivalent to the statement above.

What's happening here is the semantic analysis is bottom up, meaning `c[]` is
evaluated without regard to what context it appears in. The compiler doesn't
see that the result is being passed as `scope`, and so assumes the worst, and
issues an error.

It is not a bug in the compiler.

Trying to add some form of top down in addition to bottom up is a huge increase
in complexity, and will produce all kinds of weird corner cases. You can reopen
it as an enhancement request if you prefer, but I don't think it is practical
to implement at least in the near future.

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[Issue 17763] [scope][DIP1000] The compiler treats implicit and explicit static array slicing differently

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17763

Walter Bright  changed:

   What|Removed |Added

 CC||bugzi...@digitalmars.com

--- Comment #2 from Walter Bright  ---
(In reply to ZombineDev from comment #1)
> While previous case was rejects-valid, here's a similar one where the
> compile accepts invalid code:

Reducing the case to:

  struct Context { char[] str; }

  void main() {
Context[1] c;
use(c);
  }

  Context[] global;

  void use(scope ref Context[1] c) @safe {
global = c[];
global = c;
  }

and compiling with no flags:

  test1.d(13): Error: address of variable c assigned to global with longer
lifetime
  test1.d(14): Error: address of variable c assigned to global with longer
lifetime

compiling with -dip1000:

  test1.d(13): Error: cannot take address of scope parameter c in @safe
function use
  test1.d(14): Error: address of variable c assigned to global with longer
lifetime

The different messages are because of the different order things happen due to
the rewriting. But the error messages are still there and are correct.

Perhaps you're testing with an older compiler?

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[Issue 17763] [scope][DIP1000] The compiler treats implicit and explicit static array slicing differently

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17763

ZombineDev  changed:

   What|Removed |Added

Summary|[scope][DIP1000] Error: |[scope][DIP1000] The
   |"cannot take address of |compiler treats implicit
   |scope local" while passing  |and explicit static array
   |a slice to a scope  |slicing differently
   |parameter   |

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