Add static asserts

Author: Dobiasd

include/fplus/numeric.hpp

@@ -838,6 +838,8 @@ std::function<X(X)> divide_by(const X& x)
 // div_pos_int_ceil(5, 3) == 2
 template<typename X>
 static auto div_pos_int_ceil(X numerator, X denominator) {
+    static_assert(std::is_integral<X>::value, "type must be integral");
+    static_assert(!std::is_signed<X>::value, "type must be unsigned");
     return numerator / denominator + (numerator % denominator != 0);
 }
 

include_all_in_one/include/fplus/fplus.hpp

@@ -8352,10 +8352,12 @@ std::function<X(X)> divide_by(const X& x)
 }
 
 // API search type: div_pos_int_ceil : (a, a) -> a
-// Integer division, but rounding up instead of down.
+// Positive integer division, but rounding up instead of down.
 // div_pos_int_ceil(5, 3) == 2
 template<typename X>
 static auto div_pos_int_ceil(X numerator, X denominator) {
+    static_assert(std::is_integral<X>::value, "type must be integral");
+    static_assert(!std::is_signed<X>::value, "type must be unsigned");
     return numerator / denominator + (numerator % denominator != 0);
 }