clang whines that static_assert(A && B) uses && with a constant operand,
but this is necessary and correct, because static_assert only takes
compile-time constant expressions. However, !!A && !!B does not warn.
Switch to !!A && !!B to silence the clang whining.
similar/main/collide.cpp:2566:63: warning: use of logical '&&' with constant operand [-Wconstant-logical-operand]
static_assert(collision_result_t<OBJ_WALL, OBJ_ROBOT>::value && collision_result_t<OBJ_ROBOT, OBJ_WALL>::value, "OBJ_WALL" " " "OBJ_ROBOT");
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