Re: Refactor compile-time assertion checks for C/C++

Michael Paquier <michael(at)paquier(dot)xyz> writes:
> On Mon, Mar 16, 2020 at 10:32:36AM -0400, Tom Lane wrote:
>> Sorry for being unclear --- I just meant that we could use do{}
>> in StaticAssertStmt for both C and C++. Although now I notice
>> that the code is trying to use StaticAssertStmt for StaticAssertExpr,
>> which you're right isn't going to do. But I think something like
>> this would work and be a bit simpler than what you proposed:
>>
>> #else
>> /* Fallback implementation for C and C++ */
>> #define StaticAssertStmt(condition, errmessage) \
>> - ((void) sizeof(struct { int static_assert_failure : (condition) ? 1 : -1; }))
>> + do { struct static_assert_struct { int static_assert_failure : (condition) ? 1 : -1; }; } while(0)
>> #define StaticAssertExpr(condition, errmessage) \
>> - StaticAssertStmt(condition, errmessage)
>> + ((void) sizeof(struct { int static_assert_failure : (condition) ? 1 : -1; }))
>> #define StaticAssertDecl(condition, errmessage) \

> C++ does not allow defining a struct inside a sizeof() call, so in
> this case StaticAssertExpr() does not work with the previous extension
> in C++. StaticAssertStmt() does the work though.

[ scratches head... ] A do{} is okay in an expression in C++ ??

regards, tom lane