On 4/19/14, 1:09 PM, Filip Pizlo wrote:
> When guarding code with macros that are always defined, such as
> ASSERT_DISABLED (it's always either 0 or 1), we have a choice between:
>
> if (!ASSERT_DISABLED) {
> // do things
> }
>
> and:
>
> #if !ASSERT_DISABLED
> // do things
> #endif
>
> I'd like to propose that /anytime the normal if would be semantically
> equivalent to the preprocessor #if, the normal if should be used/.
>
> We don't lose any compiler optimization, since even at -O0, the compiler
> will constant fold the normal if. We do gain a lot of clarity, since
> the control flow of normal if statements is subject to proper indentation.
>
> The "semantically equivalent" requirement still allows for #if to be
> used for thinngs like:
>
> - Guarding the placement of fields in a class.
> - Guarding the definitions of other macros (in the case of
> ASSERT_DISABLED, we define ASSERT in different ways guarded by #if's)
> - Guarding the definition/declaration/inclusion of entire functions,
> classes, and other top-level constructs.
This is adding complexity for little gain.
I would not mind replacing all the macros by real if() branches, but
that is not possible in plenty of cases. Using both the branches and the
macro seems like a bad idea.
Benjamin
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