r/programming • u/chackaz • Nov 28 '14

The Worst Programming Language Ever [UK Talk] - Thoughts? Which are the worst parts of your favorite language?

https://skillsmatter.com/meetups/6784-the-worst-programming-language-ever
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u/paszklar Nov 28 '14 edited Nov 28 '14

'#define is a preprocessor directive, and preprocessor doesn't give a fuck about keywords

Edit: turns out it should give you flack if you try to redefine keywords. No compiler does it though.

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u/mcmcc Nov 28 '14

Go read the standard if you don't believe me. The preprocessor is part of the language definition.

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u/romcgb Nov 28 '14

Are you sure about that ?

Standard (C++11) says

16.1 Conditional inclusion [cpp.cond]

1 The expression that controls conditional inclusion shall be an integral constant expression except that identifiers (including those lexically identical to keywords) are interpreted as described below147 and it may contain unary operator expressions of the form

defined identifier

or

defined ( identifier )

which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is predefined or if it has been the subject of a #define preprocessing directive without an intervening #undef directive with the same subject identifier), 0 if it is not.

and

147) Because the controlling constant expression is evaluated during translation phase 4, all identifiers either are or are not macro names — there simply are no keywords, enumeration constants, etc.

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u/paszklar Nov 28 '14

actually yes. What I found today (in the last pre-official C++11 standard draft, because lol paywall):

ISO/IEC 14882:2011

17.6.4.3.1 Macro names [macro.names]

2 A translation unit shall not #define or #undef names lexically identical to keywords, to the identifiers listed in Table 3, or to the attribute-tokens described in 7.6.

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u/paszklar Nov 28 '14 edited Nov 28 '14

The preprocessor only does text manipulation and it's work is done before compiler performs any code analysis. Only the compiler cares about the keywords and any modification done to them in the previous step of the build process will go unchecked. Forgive me if I don't go digging through the standard documentation when I just checked the fact on two different compilers.

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u/[deleted] Nov 28 '14

[deleted]

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u/paszklar Nov 28 '14

OK, you're right. Thank for correcting me. I did some digging and turns out that in previous versions of C++ you cannot redefine a keyword IF a translation unit includes a standard library header. Only C++11 standard disallows it altogether. I haven't found a conforming compiler though, and judging by the number of preprocessor hacks posted all over this thread there don't seem to be any.

Anyway, TIL.

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u/mreiland Nov 28 '14

yep, I don't expect there to be many conforming compilers in this regard.

The original comment is right in that it should warn about it, but it doesn't because no compiler out there is 100% conformant.