http://d.puremagic.com/issues/show_bug.cgi?id=3789

           Summary: comparing a struct with an array member does a bitwise
                    compare
           Product: D
           Version: 2.040
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: schveiguy@yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-02-09 12:08:23 PST ---
If you have a struct that does not define opEquals, but which contains a member that defines opEquals, that member's opEquals is called when comparing the struct.

However, arrays are still bitwise compared.  Example:

struct String
{
    char[] data;
}

void main ()
{
    auto foo = String("foo".dup);
    auto bar = String("foo".dup);

    assert(bar.data == foo.data);
    assert(bar == foo, "oops structs aren't equal");
}

results in the second assert failing.

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
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                 CC|                            |clugdbug@yahoo.com.au


--- Comment #1 from Don <clugdbug@yahoo.com.au> 2010-02-09 13:53:32 PST ---
Arrays don't have a an opEquals overloaded operator. What's the bug?

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--- Comment #2 from Steven Schveighoffer <schveiguy@yahoo.com> 2010-02-09 14:37:33 PST ---
that is an unimportant technical difference.  The semantic meaning of the feature is that if you have a type T, and a struct S fully defined as:

struct S
{
  T member;
}

Then this assert should always pass:

S s1, s2;
... // initialize s1 and s2 to whatever you want
assert((s1 == s2) is (s1.member == s2.member));

Bitwise compare happens to be the comparison operator for all builtins except for floating point and arrays.  Although opEquals isn't defined, they certainly have special comparison operators, and those should be invoked when comparing containing structs.  This is the principle of least surprise, especially when arrays back types like strings.

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iorlas <denis.tomilin@gmail.com> changed:

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                 CC|                            |denis.tomilin@gmail.com


--- Comment #3 from iorlas <denis.tomilin@gmail.com> 2010-02-09 18:31:35 PST ---
(In reply to comment #1)
> Arrays don't have a an opEquals overloaded operator. What's the bug?

Not a bug, only not implemented part of comparison.
Ofc it must be. Throws error or comparison each element through opEqual of
elements type.

Maybe now its not a critical, but in future it can block some code.

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

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                 CC|                            |dsimcha@yahoo.com


--- Comment #4 from Simen Kjaeraas <simen.kjaras@gmail.com> 2011-02-03 04:40:42 PST ---
*** Issue 5313 has been marked as a duplicate of this issue. ***

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

           What    |Removed                     |Added
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                 CC|                            |dsimcha@yahoo.com
                 CC|                            |simen.kjaras@gmail.com


--- Comment #4 from Simen Kjaeraas <simen.kjaras@gmail.com> 2011-02-03 04:40:42 PST ---
*** Issue 5313 has been marked as a duplicate of this issue. ***

--- Comment #5 from Simen Kjaeraas <simen.kjaras@gmail.com> 2011-02-03 04:40:44 PST ---
*** Issue 4988 has been marked as a duplicate of this issue. ***

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code
            Version|2.040                       |D2
            Summary|comparing a struct with an  |Structs members that
                   |array member does a bitwise |require non-bitwise
                   |compare                     |comparison not correctly
                   |                            |compared
           Severity|normal                      |major


--- Comment #6 from Simen Kjaeraas <simen.kjaras@gmail.com> 2011-02-03 04:42:24 PST ---
Making this the main bug for erroneous bitwise comparison of structs. There were at least 4 in total.

List of things that do not work:

floating-point members
array members (including strings)

List of things that do work:

any member that uses bitwise comparison
member structs that have overloaded opEquals

The latter suggests that this should work for floating point numbers and arrays too.

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bearophile_hugs@eml.cc changed:

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                 CC|                            |bearophile_hugs@eml.cc


--- Comment #7 from bearophile_hugs@eml.cc 2011-02-04 12:17:46 PST ---
Maybe issue 5519 should be merged with this one.

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--- Comment #8 from Simen Kjaeraas <simen.kjaras@gmail.com> 2011-02-04 13:52:43 PST ---
*** Issue 5519 has been marked as a duplicate of this issue. ***

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--- Comment #9 from Kenji Hara <k.hara.pg@gmail.com> 2011-10-13 23:22:29 PDT ---
*** Issue 6812 has been marked as a duplicate of this issue. ***

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