replace enable_if in template for rank check by `xt::get_rank`

GNU GCC was complaining about a missing type definition ("no type name
'type' in 'struct::enable_if<false, int>'") for the false case
(as explained here https://stackoverflow.com/a/12625334). So given that
there are two/three false conditions for `evald`/`evalp`, it seemed
better to drop these rank checks from the templates, and use the
function `xt::get_rank` instead.

include/evalhyd/evald.hpp

@@ -3,7 +3,6 @@
 
 #include <unordered_map>
 #include <vector>
-#include <type_traits>
 
 #include <xtensor/xexpression.hpp>
 #include <xtensor/xtensor.hpp>
@@ -145,9 +144,7 @@ namespace evalhyd
     ///       evalhyd::evald(obs, prd, {"NSE"}, "none", 1, -9, msk);
     ///
     /// \endrst
-    template <class D2, class B2,
-              std::enable_if_t<xt::has_rank_t<D2, 2>::value, int> = 0,
-              std::enable_if_t<xt::has_rank_t<B2, 2>::value, int> = 0>
+    template <class D2, class B2>
     std::vector<xt::xarray<double>> evald(
             const xt::xexpression<D2>& q_obs,
             const xt::xexpression<D2>& q_prd,
@@ -162,6 +159,20 @@ namespace evalhyd
             const std::vector<std::string>& dts = {}
     )
     {
+        // check ranks of tensors
+        if (xt::get_rank<D2>::value != 2)
+        {
+            throw std::runtime_error(
+                    "observations and/or predictions are not two-dimensional"
+            );
+        }
+        if (xt::get_rank<B2>::value != 2)
+        {
+            throw std::runtime_error(
+                    "temporal masks are not two-dimensional"
+            );
+        }
+
         // retrieve real types of the expressions
         const D2& q_obs_ = q_obs.derived_cast();
         const D2& q_prd_ = q_prd.derived_cast();

include/evalhyd/evalp.hpp

@@ -3,7 +3,6 @@
 
 #include <unordered_map>
 #include <vector>
-#include <type_traits>
 
 #include <xtensor/xexpression.hpp>
 #include <xtensor/xtensor.hpp>
@@ -123,10 +122,7 @@ namespace evalhyd
     ///       evalhyd::evalp(obs, prd, {"CRPS"});
     ///
     /// \endrst
-    template <class D2, class D4, class B4,
-              std::enable_if_t<xt::has_rank_t<D2, 2>::value, int> = 0,
-              std::enable_if_t<xt::has_rank_t<D4, 4>::value, int> = 0,
-              std::enable_if_t<xt::has_rank_t<B4, 4>::value, int> = 0>
+    template <class D2, class D4, class B4>
     std::vector<xt::xarray<double>> evalp(
             const xt::xexpression<D2>& q_obs,
             const xt::xexpression<D4>& q_prd,
@@ -139,6 +135,26 @@ namespace evalhyd
             const std::vector<std::string>& dts = {}
     )
     {
+        // check ranks of tensors
+        if (xt::get_rank<D2>::value != 2)
+        {
+            throw std::runtime_error(
+                    "observations and/or thresholds are not two-dimensional"
+            );
+        }
+        if (xt::get_rank<D4>::value != 4)
+        {
+            throw std::runtime_error(
+                    "predictions are not four-dimensional"
+            );
+        }
+        if (xt::get_rank<B4>::value != 4)
+        {
+            throw std::runtime_error(
+                    "temporal masks are not four-dimensional"
+            );
+        }
+
         // retrieve real types of the expressions
         const D2& q_obs_ = q_obs.derived_cast();
         const D4& q_prd_ = q_prd.derived_cast();