apply constexpr if

source/gui/widgets/spinbox.cpp

@@ -82,10 +82,39 @@ namespace nana
 
 				bool check_value(const std::string& str) const override
 				{
+#ifdef _nana_cxx_constexpr_if
+					auto i = str.c_str();
+					if ('+' == *i || '-' == *i)
+						++i;
+
+					if constexpr(std::is_same<T, int>::value)
+					{
+						for (; 0 != *i; ++i)
+						{
+							if (*i < '0' || '9' < *i)
+								return false;
+						}
+					}
+					else
+					{
+						bool dot = false;
+						for (; 0 != *i; ++i)
+						{
+							if (('.' == *i) && (!dot))
+							{
+								dot = true;
+								continue;
+							}
+
+							if (*i < '0' || '9' < *i)
+								return false;
+						}
+					}
+#else
 					if (str.empty())
 						return true;
 
-					auto size = str.size();
+					auto const size = str.size();
 					std::size_t pos = 0;
 					if (str[0] == '+' || str[0] == '-')
 						pos = 1;
@@ -115,6 +144,7 @@ namespace nana
 								return false;
 						}
 					}
+#endif
 					return true;
 				}