[Issue 1341] New: typeof(int) should probably be legal

[Issue 1341] typeof(X) accepted, even if X is a type

Jul 03, 2008

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Jul 09, 2008

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Jul 09, 2008

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Jul 10, 2008

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July 14, 2007

[Issue 1341] New: typeof(int) should probably be legal

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http://d.puremagic.com/issues/show_bug.cgi?id=1341

           Summary: typeof(int) should probably be legal
           Product: D
           Version: 1.018
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: clugdbug@yahoo.com.au


According to the spec (in declaration.html), the argument to typeof() must be an expression. This is not currently enforced by DMD. In fact, it can be any type, except for builtin types which fail with a misleading error message.

alias int foo;
typeof(foo) a; // ok
typeof(int) b; // FAILS: found ')' when expecting '.' following 'int'

typeof(typeof(foo)) c; // ok, even though the argument is obviously a type.

I think that the compiler's behaviour generally makes more sense than the spec (and I'm finding it to be useful behaviour). Enforcing the rule in the spec would mean the compiler would need to determine if 'foo' is a type name before issuing a syntax error --> violation of independence of syntax and semantic passes.

So I suggest that the spec be changed to allow typeof(Type) to be legal, and to
adjust the compiler to accept built-in types.
eg, make typeof(int) synonymous with int.


--

http://d.puremagic.com/issues/show_bug.cgi?id=1341 smjg@iname.com changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |smjg@iname.com Keywords| |accepts-invalid, spec ------- Comment #1 from smjg@iname.com 2007-10-21 10:58 ------- According to the spec, typeof(typeof(foo)) shouldn't compile. As you've probably noticed already, the syntax is Typeof: typeof ( Expression ) and this is parseable only as a type and not as an expression. I can see that there might be some generic programming use in defining typeof(X) == X if X is already a type. The only problem is that it isn't documented. But if what's in the brackets is already not parseable as an Expression, there's no benefit to writing it this way. As such, it's probably reasonable to disallow it as it would mean yet another ambiguity in the grammar. --

http://d.puremagic.com/issues/show_bug.cgi?id=1341 ------- Comment #3 from clugdbug@yahoo.com.au 2008-07-02 02:10 ------- So the resolution would be that: typeof(X) would generate an error late in the semantic pass if X turns out to be a type, rather than an expression? --

http://d.puremagic.com/issues/show_bug.cgi?id=1341 ------- Comment #5 from clugdbug@yahoo.com.au 2008-07-03 08:03 ------- One thing worries me about this... in D1.0, a common metaprogramming idiom is "is(typeof(xxx))" For example, this compiles in D1.0: ------ static assert(!is(typeof(nonexistent))); ------ Lots of code (including BLADE, for example) will fail if that stops working. Please make sure that doesn't get broken in fixing this bug! --

http://d.puremagic.com/issues/show_bug.cgi?id=1341 clugdbug@yahoo.com.au changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|typeof(int) should probably |typeof(X) accepted, even if |be legal |X is a type ------- Comment #7 from clugdbug@yahoo.com.au 2008-07-03 09:46 ------- Changed the description of this bug in view of the discussion above. The fear I mentioned above is probably irrational. --

http://d.puremagic.com/issues/show_bug.cgi?id=1341 clugdbug@yahoo.com.au changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |RESOLVED Resolution| |FIXED ------- Comment #8 from clugdbug@yahoo.com.au 2008-07-09 07:19 ------- Fixed DMD1.032 --

http://d.puremagic.com/issues/show_bug.cgi?id=1341 clugdbug@yahoo.com.au changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |aarti@interia.pl ------- Comment #9 from clugdbug@yahoo.com.au 2008-07-09 07:20 ------- *** Bug 1777 has been marked as a duplicate of this bug. *** --

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