Create PERL_UNIQUE_NAME and use it to avoid name collisions

[khwilliamson]

PERL_UNIQUE_NAME is a factory creating a preprocessor symbol that is based on an input skeleton name, and the line number it is called from. The skeleton name would likely be something like sv1_ or PL_sv1. These should be chosen to not have conflicts with the XS code. The advantage of this approach is that you won't be using the same variable name in a bunch of macros and they collide.

• This set of changes does not require a perldelta entry.

[Leont]

Both of these make me wonder if they wouldn't be better off as an inline function.

[jkeenan]

Both of these make me wonder if they wouldn't be better off as an inline function.

@khwilliamson could you respond to the above? Thanks.

[khwilliamson]

There is a difference of opinion between people who like macros, and those who like inline functions. I was always taught that inline functions were more precious than macros, so should be avoided. No one has ever said to me that this is wrong nowadays.

So, I've changed this from the original commit, by using a factory macro to spew out unique names. And, I've only converted one macro to use it.

My principal objection to using macros over inline functions is that there can be name collisions with the arguments, and to avoid this, the names that are declared inside the macro get long and unwieldy; hard to read.

This p.r. pretty much makes that a non-issue. You can create your own short name using good naming practices, and it will expand to something unique, and if you collide with another short name, the compiler will warn you.

My principal objection to using inline functions over macros, is that I was taught these were a precious commodity; that most compilers had a very finite limit as to how many it would actually look at and inline. I think this p.r. solves that

[tonycoz]

I noticed this when looking for the OpTYPE_set() source (looking at @scottchiefbaker's uinteger) - it has the same problem as was mentioned elsewhere, o1_ and type1_ are replaced globally, if someone is using a trailing underscore for structure members, this is going to replace them with line specific nonsense.

You could handle this by using two macros, something like (untested):

#define OpTYPE_set_(o,type, o1, type1)                      \
    STMT_START {                                \
        OP *o1 = (OP *)o;                      \
        OPCODE type1 = type;                   \
        o1_->op_type = type1;                  \
        o1_->op_ppaddr = PL_ppaddr[type1];     \
    } STMT_END

#define OpTYPE_set(o, type) OpTYPE_set_(o, type, PERL_UNIQUE_NAME(o_temp), PERL_UNIQUE_NAME(type_temp))

Doing this limits the visibility of the replacement to the macro body.

Or we can use an inline function.