Variable length field in repeating group c++ compilation error

[solarprime]

No. The specification does not allow for variable length fields in a composite.

Variable length fields can be added at the end of a repeating group or the end of a message. You can compose something more complex with repeating groups or multiple messages.

Originally posted by @mjpt777 in #485 (comment)

There seems to be an issue with the generated c++ code when adding a variable length field inside a repeating group. The computeLength function is marked constexpr but calls std::vector<>::size(), which is a non-constexpr function.

    <sbe:message name="MyMessage" id="1" >
        <field name="sessionId" id="1" type="SessionId"/>
        <field name="method" id="2" type="Method"/>
        <group name="extraSendHeaders" id="5" dimensionType="groupSizeEncoding">
            <field name="headerKey" id="6" type="HeaderEnum"/>
            <data name="headerValue" id="7" type="varStringEncoding"/>
        </group>
    </sbe:message>

SBE_NODISCARD static SBE_CONSTEXPR_14 size_t computeLength(const std::vector<std::tuple<std::size_t>>& extraSendHeadersItemLengths = {})
{
#if defined(__GNUG__) && !defined(__clang__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wtype-limits"
#endif
    size_t length = sbeBlockLength();


    length += ExtraSendHeaders::sbeHeaderSize();
    if (extraSendHeadersItemLengths.size() > 65534)
    {
        throw std::runtime_error("extraSendHeadersItemLengths.size() outside of allowed range [E110]");
    }
    for (const auto& e: extraSendHeadersItemLengths)
    {
        #if __cpluplus >= 201703L
        length += std::apply(ExtraSendHeaders::computeLength, e);
        #else
        length += ExtraSendHeaders::computeLength(std::get<0>(e));
        #endif
    }
    return length;
#if defined(__GNUG__) && !defined(__clang__)
#pragma GCC diagnostic pop
#endif
}

[solarprime]

Verified that compilation of the SBE tests fail with -std=c++14 and -std=c++17.

[ 41%] Built target codecs
In file included from ~/simple-binary-encoding/sbe-samples/src/main/cpp/GeneratedStubExample.cpp:24:
~/simple-binary-encoding/cppbuild/Release/generated/cpp/baseline/Car.h: In static member function ‘static constexpr size_t baseline::Car::computeLength(const std::vector<std::tuple<long unsigned int> >&, const std::vector<std::tuple<long unsigned int> >&, std::size_t, std::size_t, std::size_t)’:
~/simple-binary-encoding/cppbuild/Release/generated/cpp/baseline/Car.h:2991:36: error: call to non-‘constexpr’ function ‘std::vector<_Tp, _Alloc>::size_type std::vector<_Tp, _Alloc>::size() const [with _Tp = std::tuple<long unsigned int>; _Alloc = std::allocator<std::tuple<long unsigned int> >; std::vector<_Tp, _Alloc>::size_type = long unsigned int]’
 2991 |     if (fuelFiguresItemLengths.size() > 65534)
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~

[tmontgomery]

SBE_CONSTEXPR_14 has been removed in 494b00a

[solarprime]

Thanks Todd.