• Thomas Kuehne <thomas-dloop kuehne.cn> Jul 19 2006
• Bruno Medeiros <brunodomedeirosATgmail SPAM.com> Jul 20 2006

Thomas Kuehne <thomas-dloop kuehne.cn> writes:

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The following isn't exactly a bug - the documentation doesn't state how
TypeInfo objects are compared - but it is an irritating behaviour:

#
# int x;
#
# bool b1 = (typeid(typeof(x)) != typeid(int));
#
# TypeInfo t1 = typeid(typeof(x));
# TypeInfo t2 = typeid(int);
#
# bool b2 = (t1 != t2);
#
# assert(b1 == b2); // FAILS
#

Thomas


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Bruno Medeiros <brunodomedeirosATgmail SPAM.com> writes:

Thomas Kuehne wrote:
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 Hash: SHA1
 
 The following isn't exactly a bug - the documentation doesn't state how
 TypeInfo objects are compared - but it is an irritating behaviour:
 
 #
 # int x;
 #
 # bool b1 = (typeid(typeof(x)) != typeid(int));
 #
 # TypeInfo t1 = typeid(typeof(x));
 # TypeInfo t2 = typeid(int);
 #
 # bool b2 = (t1 != t2);
 #
 # assert(b1 == b2); // FAILS
 #
 
 Thomas
 
 
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 =N9M0
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It's a bug. Consider:

   writefln( typeid(int) == typeid(int) ); // prints true
   writefln( typeid(int) != typeid(int) ); // also prints true! INCORRECT

Which can't be right, == and != can't give the same results for the same 
operands. The bug is in the constant folding(evaluation) system: if we 
the check the asm for that code then 1(true) is generated for both 
calls. Also, the following code, which are runtime evaluations, work 
correctly:

   auto t1 = typeid(int);
   writefln( t1 == t1 ); // prints 1
   writefln( t1 != t1 ); // prints false
   writefln( t1 == typeid(int) ); // prints 1
   writefln( t1 != typeid(int) ); // prints false


-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D