Hacker News Reader

Comment by sanxiyn | Hacker News Reader

This doesn't seem to allow single line if or while statements, because parentheses are optional.

I like single line if when it is appropriate. (Python allows single line if by using colons.) Apart from my taste, C preprocessor macros can't expand to more than a single line, so this seems to prevent macros expanding to contain control structures. Is there an easy fix?

View on HN

You could do it by separating the body with a semicolon:

    if something_is_true(); log("warning!")

I haven't really considered the preprocessor as I prefer to avoid it as much as possible.

This doesn't work. "if a; if b; c; d" is then an ambiguous parse to both "if (a) { if (b) { c; d; } }" and "if (a) { if (b) { c; } d; }". If you decide to parse one way, how do you write the other one in a single line?

I'd make this parse as "if (a) { if (b) { c; d; } }" and leave it at that. One of the reasons for significant indentation is to discourage this kind of code layout because it's hard to read.

Okay, concretely, I'd like to see a translation of this real-world C++ code (taken from V8):

  #define RETURN_OBJECT_UNLESS_EXCEPTION(ISOLATE, RETURN_VALUE, RETURN_EMPTY) \
    if (!__allocation__.IsRetry()) {                                          \
      __object__ = __allocation__.ToObjectChecked();                          \
      if (__object__ == (ISOLATE)->heap()->exception()) { RETURN_EMPTY; }     \
      RETURN_VALUE;                                                           \
    }

This seems to be missing backslashes. I haven't considered how to deal with preprocessor macros, but the if statement converts very simply:

    if !__allocation__.IsRetry()
        __object__ = __allocation__.ToObjectChecked()
        if __object__ == (ISOLATE)->heap()->exception(); RETURN_EMPTY
        RETURN_VALUE

This isn't ambiguous like the example you suggested before.

That doesn't work, because if statement is inside preprocessor macro and must be in a single line.

I see what you mean. Yes, the if in a macro is a problem. I haven't addressed macros, that's a whole different can of worms.

But you can extend lines by putting a \ at the end. I think I was this while looking through some glibc code quite a long time ago. So, you can have a single "line" that happens to have multiple statements.

Reply on news.ycombinator.com