code: func (v *MrbValue) SetInstanceVariable(variable string, value *MrbValue) {
  	cs := C.CString(variable)
  	defer C.free(unsafe.Pointer(cs))
  	C._go_mrb_iv_set(v.state, v.value, C.mrb_intern_cstr(v.state, cs), value.value)
  }
docs: // SetInstanceVariable sets an instance variable on this value.