追ってみたけど。。。うーん。。。わかんね。

(gdb) file ix.exe
(gdb) run
ix:001>Foo: class(Class) {}

Program received signal SIGSEGV, Segmentation fault.
0x004c6fe2 in xtal::pvalue (v=@0x44) at ../xtal/xtal_any.h:237
237                     return v.pvalue_;
(gdb) bt
#0  0x004c6fe2 in xtal::pvalue (v=@0x44) at ../xtal/xtal_any.h:237
#1  0x004d0d75 in xtal::SmartPtr<xtal::Array>::get2 (this=0x44)
    at ../xtal/xtal_smartptr.h:256
#2  0x004d0d60 in xtal::SmartPtr<xtal::Array>::get (this=0x44)
    at ../xtal/xtal_smartptr.h:244
#3  0x004d0d89 in xtal::SmartPtr<xtal::Array>::operator-> (this=0x44)
    at ../xtal/xtal_smartptr.h:233
#4  0x0040b882 in xtal::Class::is_inherited (this=0x0, v=@0x1363e28)
    at ../xtal/xtal_frame.cpp:448
#5  0x0042738c in xtal::Any::is (this=0x137afa0, v=@0x1363e28)
    at ../xtal/xtal_any.cpp:253
#6  0x0040203f in xtal::cast_helper_helper_extend_any (a=@0x137afa0,
    cls=@0x1363e28) at ../xtal/xtal_cast.cpp:81
#7  0x00498fce in xtal::cast_helper_helper<xtal::Class, xtal::SmartPtr<xtal::Cla
ss> const*> (a=@0x137afa0) at ../xtal/xtal_cast.h:86
#8  0x004866cb in xtal::CastHelper<xtal::SmartPtr<xtal::Class> const*>::cast_inn
er<xtal::SmartPtr<xtal::Class> const> (a=@0x137afa0)
    at ../xtal/xtal_cast.h:180
#9  0x0048673d in xtal::CastHelper<xtal::SmartPtr<xtal::Class> const*>::cast (
    a=@0x137afa0) at ../xtal/xtal_cast.h:217
#10 0x0049e815 in xtal::cast<xtal::SmartPtr<xtal::Class> const*> (
    a=@0x137afa0) at ../xtal/xtal_cast.h:247
#11 0x004861a5 in xtal::CastHelper<xtal::SmartPtr<xtal::Class> >::cast_inner (
    a=@0x137afa0) at ../xtal/xtal_cast.h:207
#12 0x004861dd in xtal::CastHelper<xtal::SmartPtr<xtal::Class> >::cast (
    a=@0x137afa0) at ../xtal/xtal_cast.h:217
#13 0x0049e769 in xtal::cast<xtal::SmartPtr<xtal::Class> > (a=@0x137afa0)
    at ../xtal/xtal_cast.h:247
#14 0x0043f2c6 in xtal::VMachine::FunClassBegin (this=0x136b508,
    pc=0x1362bd3 "\206") at ../xtal/xtal_vmachine.cpp:2992
#15 0x004379bb in xtal::VMachine::execute_inner (this=0x136b508,
    start=0x1362bd0 "y") at ../xtal/xtal_vmachine.cpp:1996
#16 0x00433955 in xtal::VMachine::execute (this=0x136b508, fun=0x1381df0,
    start_pc=0x1362bd0 "y") at ../xtal/xtal_vmachine.cpp:392
#17 0x004544cc in xtal::CodeBuilder::interactive_compile (this=0x22a560)
    at ../xtal/xtal_codebuilder.cpp:99
#18 0x00418b02 in xtal::ix () at ../xtal/xtal_lib.cpp:72
#19 0x0040181b in main (argc=1, argv=0x1361c18) at ../xtal/ixmain.cpp:31

フレーム #4 の this が NULL になってるのがこの現象の要因だろうけど、なんで NULL になるのかよーわからん。

#4  0x0040b882 in xtal::Class::is_inherited (this=0x0, v=@0x1363e28)

こまった。