GenerateInstantiations.hpp
1 // Distributed under the MIT License.
2 // See LICENSE.txt for details.
3 
4 #pragma once
5 
6 // IWYU pragma: begin_exports
7 #include <boost/parameter/name.hpp>
8 #include <boost/preprocessor/arithmetic/inc.hpp>
9 #include <boost/preprocessor/control/expr_iif.hpp>
10 #include <boost/preprocessor/control/iif.hpp>
11 #include <boost/preprocessor/control/while.hpp>
12 #include <boost/preprocessor/list/adt.hpp>
13 #include <boost/preprocessor/list/fold_left.hpp>
14 #include <boost/preprocessor/list/fold_right.hpp>
15 #include <boost/preprocessor/list/for_each_product.hpp>
16 #include <boost/preprocessor/list/size.hpp>
17 #include <boost/preprocessor/list/to_tuple.hpp>
18 #include <boost/preprocessor/list/transform.hpp>
19 #include <boost/preprocessor/logical/bitand.hpp>
20 #include <boost/preprocessor/logical/bool.hpp>
21 #include <boost/preprocessor/logical/compl.hpp>
22 #include <boost/preprocessor/repetition/for.hpp>
23 #include <boost/preprocessor/tuple/elem.hpp>
24 #include <boost/preprocessor/tuple/reverse.hpp>
25 #include <boost/preprocessor/tuple/size.hpp>
26 #include <boost/preprocessor/tuple/to_list.hpp>
27 #include <boost/preprocessor/variadic/elem.hpp>
28 #include <boost/preprocessor/variadic/to_list.hpp>
29 // IWYU pragma: end_exports
30 
31 /// \cond
32 #define GENERATE_INSTANTIATIONS_DO_PRODUCT(INSTANTIATION_MACRO, LIST_OF_LISTS) \
33  BOOST_PP_LIST_FOR_EACH_PRODUCT(INSTANTIATION_MACRO, \
34  BOOST_PP_LIST_SIZE(LIST_OF_LISTS), \
35  BOOST_PP_LIST_TO_TUPLE(LIST_OF_LISTS))
36 
37 #define GENERATE_INSTANTIATION_TUPLES_TO_LISTS(d, _, elem) \
38  BOOST_PP_TUPLE_TO_LIST(BOOST_PP_TUPLE_SIZE(elem), elem)
39 /// \endcond
40 
41 /*!
42  * \ingroup UtilitiesGroup
43  * \brief Macro useful for generating many explicit instantiations of function
44  * or class templates
45  *
46  * It is often necessary to generate explicit instantiations of function or
47  * class templates. Since the total number of explicit instantiations scales as
48  * the product of the number of possible number of parameter values of each
49  * template parameter, this quickly becomes tedious. This macro allows you to
50  * easily generate hundreds of explicit instantiations.
51  *
52  * The first argument to the macro is a macro that takes two arguments and is
53  * described below. The remaining arguments are macro-tuples, e.g. `(1, 2, 3)`.
54  * The Cartesian product of the macro-tuples is then computed and each term is
55  * passed as a tuple as the second argument to the `INSTANTIATION_MACRO`. The
56  * first argument to the `INSTANTIATION_MACRO` is a Boost.Preprocessor internal
57  * variable so just make it `_`. The `INSTANTIATION(_, data)` macro below serves
58  * as an example. A concrete example is generating explicit instantiations of
59  * the class `Index<Dim>` for `Dim = 0,1,2,3`, which you would do as follows:
60  *
61  * \code
62  * #define GET_DIM(data) BOOST_PP_TUPLE_ELEM(0, data)
63  *
64  * #define INSTANTIATION(_, data) \
65  * template class Index<GET_DIM(data)>;
66  *
67  * GENERATE_INSTANTIATIONS(INSTANTIATION, (0, 1, 2, 3))
68  *
69  * #undef GET_DIM
70  * #undef INSTANTIATION
71  * \endcode
72  *
73  * This will generate:
74  *
75  * \code
76  * template class Index<0>;
77  * template class Index<1>;
78  * template class Index<2>;
79  * template class Index<3>;
80  * \endcode
81  *
82  * It is also possible to generate explicit instantiations for multiple classes
83  * or functions in a single call to `GENERATE_INSTANTIATIONS`. For example, the
84  * (in)equivalence operators can be generated using:
85  *
86  * \code
87  * #define GET_DIM(data) BOOST_PP_TUPLE_ELEM(0, data)
88  * #define GEN_OP(op, dim) \
89  * template bool operator op(const Index<dim>& lhs, \
90  * const Index<dim>& rhs) noexcept;
91  * #define INSTANTIATION(_, data) \
92  * template class Index<GET_DIM(data)>; \
93  * GEN_OP(==, GET_DIM(data)) \
94  * GEN_OP(!=, GET_DIM(data))
95  *
96  * GENERATE_INSTANTIATIONS(INSTANTIATION, (0, 1, 2, 3))
97  *
98  * #undef GET_DIM
99  * #undef GEN_OP
100  * #undef INSTANTIATION
101  * \endcode
102  *
103  * which will result in the instantiations:
104  *
105  * \code
106  * template class Index<0>;
107  * template bool operator==(const Index<0>& lhs, const Index<0>& rhs) noexcept;
108  * template bool operator!=(const Index<0>& lhs, const Index<0>& rhs) noexcept;
109  * template class Index<1>;
110  * template bool operator==(const Index<1>& lhs, const Index<1>& rhs) noexcept;
111  * template bool operator!=(const Index<1>& lhs, const Index<1>& rhs) noexcept;
112  * template class Index<2>;
113  * template bool operator==(const Index<2>& lhs, const Index<2>& rhs) noexcept;
114  * template bool operator!=(const Index<2>& lhs, const Index<2>& rhs) noexcept;
115  * template class Index<3>;
116  * template bool operator==(const Index<3>& lhs, const Index<3>& rhs) noexcept;
117  * template bool operator!=(const Index<3>& lhs, const Index<3>& rhs) noexcept;
118  * \endcode
119  *
120  * Now let's look at generating instantiations of member function templates of
121  * class templates, which will be a common use case. In this example we generate
122  * explicit instantiations of all the member function templates of the class
123  * `ScalarWave::Solutions::PlaneWave`. In total, for `Dim = 1,2,3` and types
124  * `double` and `DataVector` this is about 42 explicit instantiations, which
125  * would be extremely annoying to write by hand. The macro code is surprisingly
126  * simple:
127  *
128  * \code
129  * #define DIM(data) BOOST_PP_TUPLE_ELEM(0, data)
130  * #define DTYPE(data) BOOST_PP_TUPLE_ELEM(1, data)
131  *
132  * #define INSTANTIATE(_, data) \
133  * template Scalar<DTYPE(data)> \
134  * ScalarWave::Solutions::PlaneWave<DIM(data)>::psi( \
135  * const tnsr::I<DTYPE(data), DIM(data)>& x, double t) const noexcept; \
136  * template Scalar<DTYPE(data)> \
137  * ScalarWave::Solutions::PlaneWave<DIM(data)>::dpsi_dt( \
138  * const tnsr::I<DTYPE(data), DIM(data)>& x, double t) const noexcept;
139  *
140  * GENERATE_INSTANTIATIONS(INSTANTIATE, (1, 2, 3), (double, DataVector))
141  *
142  * #undef DIM
143  * #undef DTYPE
144  * #undef INSTANTIATE
145  * \endcode
146  *
147  * We don't show the result from preprocessor since for all of the member
148  * functions of `PlaneWave` the total output is approximately 150 lines, but you
149  * can hopefully see the benefits of generating explicit instantiations using
150  * the `GENERATE_INSTANTIATIONS` way.
151  *
152  * One thing that can be difficult is debugging metaprograms (be they template
153  * or macro-based). To this end we provide a make target `DebugPreprocessor`
154  * which prints the output of running the preprocessor on the file
155  * `src/Executables/DebugPreprocessor/DebugPreprocessor.cpp`.
156  * Note that the output of the `GENERATE_INSTANTIATIONS` macro will be on a
157  * single line, so it often proves useful to copy-paste the output into an
158  * editor and run clang-format over the code so it's easier to reason about.
159  */
160 #define GENERATE_INSTANTIATIONS(INSTANTIATION_MACRO, ...) \
161  GENERATE_INSTANTIATIONS_DO_PRODUCT( \
162  INSTANTIATION_MACRO, \
163  BOOST_PP_LIST_TRANSFORM(GENERATE_INSTANTIATION_TUPLES_TO_LISTS, _, \
164  BOOST_PP_VARIADIC_TO_LIST(__VA_ARGS__)))