digitalmars.D.bugs - irritating opCmp behaviour for TypeInfo
- Thomas Kuehne (22/22) Jul 19 2006 -----BEGIN PGP SIGNED MESSAGE-----
- Bruno Medeiros (17/45) Jul 20 2006 It's a bug. Consider:
-----BEGIN PGP SIGNED MESSAGE----- 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: Thomas -----BEGIN PGP SIGNATURE----- iD8DBQFEvpFeLK5blCcjpWoRAuPhAJ4+NhWzk9wj0PhTl8TG0Frf7u9MsgCgl2BJ aYNPaKW3fVB71hp64z8z/Dw= =N9M0 -----END PGP SIGNATURE-----
Jul 19 2006
Thomas Kuehne wrote:-----BEGIN PGP SIGNED MESSAGE----- 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: Thomas -----BEGIN PGP SIGNATURE----- iD8DBQFEvpFeLK5blCcjpWoRAuPhAJ4+NhWzk9wj0PhTl8TG0Frf7u9MsgCgl2BJ aYNPaKW3fVB71hp64z8z/Dw= =N9M0 -----END PGP SIGNATURE-----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
Jul 20 2006