replace goto inside a macro with something else

Question

I'm attempting to remove goto statement inside Mach7, because goto is not allowed in constexpr function:

#define MatchQ(s) {                                                            \
        XTL_MATCH_PREAMBULA(s)                                                 \
        enum { __base_counter = XTL_COUNTER };                                 \
        typedef mch::unified_switch<source_type> switch_traits;                \
        XTL_PRELOADABLE_LOCAL_STATIC(XTL_CPP0X_TYPENAME switch_traits::static_data_type,static_data,match_uid_type,XTL_EMPTY()); \
        XTL_CPP0X_TYPENAME switch_traits::local_data_type  local_data;         \
        bool processed = false;                                       \
        size_t jump_target = switch_traits::choose(subject_ptr,static_data,local_data); \
        XTL_CONCAT(ReMatch,__LINE__):                                          \
        switch (jump_target)                                                   \
        {                                                                      \
            XTL_NON_REDUNDANCY_ONLY(default:)                                  \
            { XTL_REDUNDANCY_ONLY(try){{                                       \
            if (switch_traits::on_default(jump_target,local_data,static_data)) \
                goto XTL_CONCAT(ReMatch,__LINE__);                             \
            XTL_SUBCLAUSE_FIRST

The codes above use goto here: goto XTL_CONCAT(ReMatch,__LINE__);, which is possible to jump to upside of switch statement.

How to replace goto here with something else?

Might enclosing the lines starting from XTL_CONCAT(ReMatch,LINE): all the way till the end of the closing bracket of switch with "while(true){", and then replacing "goto" statements with "break/continue" be a solution? — ozlsn
– ozlsn, Commented Feb 27, 2019 at 4:03
@ozlsn I have tried it before posting this question, but failed somehow, lemme gcc -E to dig into it. — Li Chen
– Li Chen, Commented Feb 27, 2019 at 4:31
XTL_REDUNDANCY_ONLY may set up another loop which a "continue;" would cycle through. We'd have to see all the macros. — Geoduck
– Geoduck, Commented Feb 27, 2019 at 4:33
Why do you use such complex macro's? Can't you use regular functions instead? — JVApen
– JVApen, Commented Feb 27, 2019 at 7:46
@JVApen I'm not the author of this pattern-matching library. So I cannot answer this question before get familiar enough with this library — Li Chen
– Li Chen, Commented Feb 27, 2019 at 7:49

Li Chen · Accepted Answer · 2019-02-27 07:39:36Z

0

with the help of @ozlsn and gcc -E, the replacement is done. persuade codes:

while(true)
{
    bool continue_flag = false;
    switch(var)
    {
        default:
            if(something)
                continue_flag = true;
                break;
        // do something
        OtherCases:
            // do something
    }
    if (!contine_flag)
        break;
}

full commit here: https://github.com/FirstLoveLife/Mach7/commit/3db24a337a7643018ed9e12ac95f53f9a036251c

Here is a related QA: Using continue in a switch statement

edited Feb 27, 2019 at 7:39

answered Feb 27, 2019 at 6:03

Li Chen

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