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digitalmars.D.bugs - [Issue 7539] New: cast(bool) of empty array must result in false

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7539

           Summary: cast(bool) of empty array must result in false
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: timon.gehr gmx.ch


--- Comment #0 from timon.gehr gmx.ch 2012-02-18 19:44:16 PST ---
cast(bool)array must be rewritten to cast(bool)array.length.

assert(!""); // currently fails
assert(![]); // currently passes
assert(![' '][1..1]);  // passes
assert(!" "[1..1]);    // fails

assert(a==b && (!a&&b||!b&&a)); // might fail more or less randomly for dynamic
arrays a,b

The current behavior is that cast(bool)array is translated to
cast(bool)array.ptr. This is likely a leftover from the times when dynamic
arrays implicitly converted to their .ptr properties. It does not convey any
useful semantics, yet it is invoked implicitly every time a dynamic array
appears in a boolean evaluation context.

struct DynArray{
    size_t length;
    int* ptr;
    alias ptr this;
}
void main(){
    DynArray a;
    int[] b;
    writeln(cast(bool)a); // false
    writeln(cast(bool)b); // false

    a.ptr = new    int;
    writeln(cast(bool)a); // true

    *(cast(int**)&b+1) = new int; // "b.ptr = new int"
    writeln(cast(bool)b); // true
}

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next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7539



--- Comment #1 from timon.gehr gmx.ch 2012-02-18 20:18:38 PST ---
More evidence: Currently these both fail to interpret with the same error
message.

static assert(cast(int*)[]||1);
static assert(cast(bool)[]||1);

The current semantics were an accident.

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prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=7539


bearophile_hugs eml.cc changed:

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


--- Comment #2 from bearophile_hugs eml.cc 2012-02-19 04:57:07 PST ---
See also issue 4733

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