Real-world use of X-Macros

Question

I just learned of X-Macros. What real-world uses of X-Macros have you seen? When are they the right tool for the job?

Answer 1

https://github.com/whunmr/DataEx

I am using the following xmacros to generate a C++ class, with serialize and deserialize functionality built in.

#define __FIELDS_OF_DataWithNested(_)  \
  _(1, a, int  )                       \
  _(2, x, DataX)                       \
  _(3, b, int  )                       \
  _(4, c, char )                       \
  _(5, d, __array(char, 3))            \
  _(6, e, string)                      \
  _(7, f, bool)

DEF_DATA(DataWithNested);

Usage:

TEST_F(t, DataWithNested_should_able_to_encode_struct_with_nested_struct) {
    DataWithNested xn;
    xn.a = 0xCAFEBABE;
    xn.x.a = 0x12345678;
    xn.x.b = 0x11223344;
    xn.b = 0xDEADBEEF;
    xn.c = 0x45;
    memcpy(&xn.d, "XYZ", strlen("XYZ"));

    char buf_with_zero[] = {0x11, 0x22, 0x00, 0x00, 0x33};
    xn.e = string(buf_with_zero, sizeof(buf_with_zero));
    xn.f = true;

    __encode(DataWithNested, xn, buf_);

    char expected[] = { 0x01, 0x04, 0x00, 0xBE, 0xBA, 0xFE, 0xCA,
                        0x02, 0x0E, 0x00 /*T and L of nested X*/,
                        0x01, 0x04, 0x00, 0x78, 0x56, 0x34, 0x12,
                        0x02, 0x04, 0x00, 0x44, 0x33, 0x22, 0x11,
                        0x03, 0x04, 0x00, 0xEF, 0xBE, 0xAD, 0xDE,
                        0x04, 0x01, 0x00, 0x45,
                        0x05, 0x03, 0x00, 'X', 'Y', 'Z',
                        0x06, 0x05, 0x00, 0x11, 0x22, 0x00, 0x00, 0x33,
                        0x07, 0x01, 0x00, 0x01};

    EXPECT_TRUE(ArraysMatch(expected, buf_));
}

Also, another example is in https://github.com/whunmr/msgrpc.