Perfom casts to inherited types in Rust

pineappl_cli/src/import.rs

@@ -66,7 +66,7 @@ fn convert_fastnlo(
     );
     let grid = fastnlo::convert_fastnlo_table(&file, alpha, dis_pid)?;
     let results = ffi::GetCrossSection(
-        ffi::downcast_lhapdf_to_reader_mut(file.as_mut().unwrap()),
+        ffi::static_cast_lhapdf_to_reader_mut(file.as_mut().unwrap()),
         false,
     );
 

pineappl_cli/src/import/fastnlo.rs

@@ -8,11 +8,16 @@ use pineappl::sparse_array3::SparseArray3;
 use pineappl::subgrid::{Mu2, SubgridParams};
 use pineappl_fastnlo::ffi::{
     self, fastNLOCoeffAddBase, fastNLOCoeffAddFix, fastNLOCoeffAddFlex, fastNLOLHAPDF,
-    fastNLOPDFLinearCombinations, EScaleFunctionalForm,
+    fastNLOPDFLinearCombinations, fastNLOReader, fastNLOTable, EScaleFunctionalForm,
 };
 use std::convert::{TryFrom, TryInto};
 use std::f64::consts::TAU;
 
+// needed to cast between different types that are the same in C++ through inheritance
+unsafe fn static_cast<T, U>(x: &U) -> &T {
+    &*((x as *const U) as *const T)
+}
+
 fn pid_to_pdg_id(pid: i32) -> i32 {
     match pid {
         -6..=-1 | 1..=6 => pid,
@@ -95,7 +100,7 @@ fn convert_coeff_add_fix(
     alpha: u32,
     dis_pid: i32,
 ) -> Grid {
-    let table_as_add_base = ffi::downcast_coeff_add_fix_to_base(table);
+    let table_as_add_base: &fastNLOCoeffAddBase = unsafe { static_cast(table) };
 
     let mut grid = Grid::new(
         create_lumi(table_as_add_base, comb, dis_pid),
@@ -214,7 +219,7 @@ fn convert_coeff_add_flex(
     ipub_units: i32,
     dis_pid: i32,
 ) -> Grid {
-    let table_as_add_base = ffi::downcast_coeff_add_flex_to_base(table);
+    let table_as_add_base: &fastNLOCoeffAddBase = unsafe { static_cast(table) };
 
     let mut grid = Grid::new(
         create_lumi(table_as_add_base, comb, dis_pid),
@@ -406,8 +411,8 @@ fn convert_coeff_add_flex(
 }
 
 pub fn convert_fastnlo_table(file: &fastNLOLHAPDF, alpha: u32, dis_pid: i32) -> Result<Grid> {
-    let file_as_reader = ffi::downcast_lhapdf_to_reader(file);
-    let file_as_table = ffi::downcast_lhapdf_to_table(file);
+    let file_as_reader: &fastNLOReader = unsafe { static_cast(file) };
+    let file_as_table: &fastNLOTable = unsafe { static_cast(file) };
 
     let bins: usize = file_as_table.GetNObsBin().try_into().unwrap();
     let mut grids = Vec::new();
@@ -426,7 +431,7 @@ pub fn convert_fastnlo_table(file: &fastNLOLHAPDF, alpha: u32, dis_pid: i32) ->
             break;
         }
 
-        let linear_combinations = ffi::downcast_reader_to_pdf_linear_combinations(file_as_reader);
+        let linear_combinations: &fastNLOPDFLinearCombinations = unsafe { static_cast(file) };
 
         let converted = unsafe { ffi::dynamic_cast_coeff_add_fix(coeff_base) };
 

pineappl_fastnlo/src/fastnlo.cpp

@@ -158,27 +158,7 @@ std::size_t GetNx(fastNLOCoeffAddFlex const& coeffs, std::size_t obs)
     return coeffs.GetSigmaTildes().at(0)->at(obs).size();
 }
 
-fastNLOCoeffAddBase const& downcast_coeff_add_fix_to_base(fastNLOCoeffAddFix const& coeffs)
-{
-    return coeffs;
-}
-
-fastNLOCoeffAddBase const& downcast_coeff_add_flex_to_base(fastNLOCoeffAddFlex const& coeffs)
-{
-    return coeffs;
-}
-
-fastNLOReader const& downcast_lhapdf_to_reader(fastNLOLHAPDF const& lhapdf)
-{
-    return lhapdf;
-}
-
-fastNLOReader& downcast_lhapdf_to_reader_mut(fastNLOLHAPDF& lhapdf)
-{
-    return lhapdf;
-}
-
-fastNLOTable const& downcast_lhapdf_to_table(fastNLOLHAPDF const& lhapdf)
+fastNLOReader& static_cast_lhapdf_to_reader_mut(fastNLOLHAPDF& lhapdf)
 {
     return lhapdf;
 }
@@ -203,12 +183,6 @@ fastNLOCoeffMult const* dynamic_cast_coeff_mult(fastNLOCoeffBase const* coeffs)
     return dynamic_cast <fastNLOCoeffMult const*> (coeffs);
 }
 
-fastNLOPDFLinearCombinations const& downcast_reader_to_pdf_linear_combinations(
-    fastNLOReader const& reader
-) {
-    return reader;
-}
-
 pair_double_double GetObsBinDimBounds(
     fastNLOTable const& table,
     unsigned int iObs,

pineappl_fastnlo/src/fastnlo.hpp

@@ -62,15 +62,7 @@ double GetSigmaTilde(
 
 std::size_t GetNx(fastNLOCoeffAddFlex const& coeffs, std::size_t);
 
-fastNLOCoeffAddBase const& downcast_coeff_add_fix_to_base(fastNLOCoeffAddFix const& coeffs);
-
-fastNLOCoeffAddBase const& downcast_coeff_add_flex_to_base(fastNLOCoeffAddFlex const& coeffs);
-
-fastNLOReader const& downcast_lhapdf_to_reader(fastNLOLHAPDF const& lhapdf);
-
-fastNLOReader& downcast_lhapdf_to_reader_mut(fastNLOLHAPDF& lhapdf);
-
-fastNLOTable const& downcast_lhapdf_to_table(fastNLOLHAPDF const& lhapdf);
+fastNLOReader& static_cast_lhapdf_to_reader_mut(fastNLOLHAPDF& lhapdf);
 
 fastNLOCoeffAddFix const* dynamic_cast_coeff_add_fix(fastNLOCoeffBase const* coeffs);
 
@@ -80,10 +72,6 @@ fastNLOCoeffData const* dynamic_cast_coeff_data(fastNLOCoeffBase const* coeffs);
 
 fastNLOCoeffMult const* dynamic_cast_coeff_mult(fastNLOCoeffBase const* coeffs);
 
-fastNLOPDFLinearCombinations const& downcast_reader_to_pdf_linear_combinations(
-    fastNLOReader const& reader
-);
-
 pair_double_double GetObsBinDimBounds(
     fastNLOTable const& table,
     unsigned int iObs,

pineappl_fastnlo/src/lib.rs

@@ -208,15 +208,6 @@ pub mod ffi {
             _: i32,
         ) -> f64;
 
-        fn downcast_coeff_add_fix_to_base(_: &fastNLOCoeffAddFix) -> &fastNLOCoeffAddBase;
-        fn downcast_coeff_add_flex_to_base(_: &fastNLOCoeffAddFlex) -> &fastNLOCoeffAddBase;
-        fn downcast_lhapdf_to_reader(_: &fastNLOLHAPDF) -> &fastNLOReader;
-        fn downcast_lhapdf_to_reader_mut(_: Pin<&mut fastNLOLHAPDF>) -> Pin<&mut fastNLOReader>;
-        fn downcast_lhapdf_to_table(_: &fastNLOLHAPDF) -> &fastNLOTable;
-        fn downcast_reader_to_pdf_linear_combinations(
-            _: &fastNLOReader,
-        ) -> &fastNLOPDFLinearCombinations;
-
         unsafe fn dynamic_cast_coeff_add_fix(
             _: *const fastNLOCoeffBase,
         ) -> *const fastNLOCoeffAddFix;
@@ -226,6 +217,8 @@ pub mod ffi {
         unsafe fn dynamic_cast_coeff_data(_: *const fastNLOCoeffBase) -> *const fastNLOCoeffData;
         unsafe fn dynamic_cast_coeff_mult(_: *const fastNLOCoeffBase) -> *const fastNLOCoeffMult;
 
+        fn static_cast_lhapdf_to_reader_mut(_: Pin<&mut fastNLOLHAPDF>) -> Pin<&mut fastNLOReader>;
+
         fn make_fastnlo_lhapdf_with_name_file_set(
             name: &str,
             lhapdf: &str,