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digitalmars.D.bugs - [Issue 5297] New: The lookup order of recursive with statements is undefined.

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5297

           Summary: The lookup order of recursive with statements is
                    undefined.
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: trivial
          Priority: P2
         Component: websites
        AssignedTo: nobody puremagic.com
        ReportedBy: blood.of.life gmail.com



05:27:29 PST ---
In implementing SDC I find myself asking these questions, and I wish to try and
put and end to DMD being the sole definer of semantics; just letting you know
the reason for this and subsequent bug reports.

Given a series of with statements:

    with (a) with (b) with (c) {
        d();
    }

If all three objects have a method d(), then c gets called. Obviously the with
statements are considered in a LIFO order, and the sentence

http://www.digitalmars.com/d/2.0/statement.html#WithStatement
"Use of with object symbols that shadow local symbols with the same identifier
are not allowed. "

does not apply here. Neither is documented behaviour, and the only to figure
out how D behaves is to run DMD.

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=5297


Simen Kjaeraas <simen.kjaras gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |accepts-invalid
                 CC|                            |simen.kjaras gmail.com
          Component|websites                    |DMD
           Platform|Other                       |All
            Version|unspecified                 |D2
           Severity|trivial                     |normal



PST ---
This is a compiler bug. Symbols used in with should shadow symbols from other
with statements.

You're right however, that the spec should state this.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs eml.cc





 Symbols used in with should shadow symbols from other
 with statements.


Do you mean "shouldn't"?

This shadowing is not detected, and I think the compiler has to flag this is as
a compile error (just like it does with normal variables in the function stack
frame):

struct X { int a; }
struct Y { int a; }
void main() {
    X x;
    Y y;
    with (x) {
        a = 2;
        with (y) {
            a = 1;
        }
    }
    assert(x.a == 2);
}

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PST ---




 Symbols used in with should shadow symbols from other
 with statements.


 
 Do you mean "shouldn't"?


Yes and no. It shouldn't silently do so, but it should detect that that is what
is happening, and cry out loudly.

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Walter Bright <bugzilla digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla digitalmars.com



11:29:23 PST ---
The spec looks correct to me. The lookup order is not undefined, each
successive with introduces a new scope which overrides previous scopes.

As for the shadowing, that is a bug in the compiler.

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Jan 20 2012