Re: What's the purpose of these parentheses in the #define's?

[Niccolo Medici <niccolomedici@...>]

On 1/25/15, Paige DePol <lual@serfnet.org> wrote:
> Niccolo Medici <niccolomedici@gmail.com> wrote:
>
>> lauxlib.h has:
>>
>>  #define luaL_optstring(L,n,d)  (luaL_optlstring(L, (n), (d), NULL))
>>  #define luaL_typename(L,i)     lua_typename(L, lua_type(L,(i)))
>>
>> Why are there "(n)" / "(d)" / "(i)" instead of "n" / "d" / "i"? There
>> are commas around these letters so there shouldn't be a potential
>> precedence problem there, or am I wrong?
[...]
>
> I can explain this best with a simple example:
>
> #define ackoop(a)  a * 20
>
> ackoop(5 + 7)
>
> This would expand to:
>
> 5 + 7 * 20

Yes, I know about *that*. But the macros I'm talking about look like
function calls. A comma (,) has the lowest precedence in C. So why do
we need the parentheses? Let me modify your example:

  #define ackoop(a, b)  boop(a, b)

If I do:

  ackoop(5 + 7, -6)

Everything works alright. No need for further parentheses in the macro
definition. My question is, why is the macro nevertheless defined as:

  #define ackoop(a, b)  boop((a), (b))

Why's the need for these seemingly spurious parentheses in Lua's macros?