bslmf::MakeIntegerSequence_ConcatUtil_t is an alias to the result type of the bslmf::MakeIntegerSequence_ConcatUtil meta-function.
Declared in <bslmf_makeintegersequence.h>
template<
class t_S1,
class t_S2>
using MakeIntegerSequence_ConcatUtil_t = MakeIntegerSequence_ConcatUtil<t_S1, t_S2>::type;