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The expansion of the macro m will result in the expression ++i being used as an unevaluated operand to sizeof(). However, the expectation of the programmer at the expansion loci is that i is preincremented only once. This exception still requires compliance with PRE31-C. Avoid side effects in arguments to unsafe macros.
The following code is an example of compliant code using an unevaluated operand in a SFINAE context to determine whether a type can be postfix incremented:
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