chore: example of Boost.Histogram build for quick testing (#591)

* fix: add a little extra testing for repr and empty axes

* chore: supply a little helper for checking C++ boost-histogram

* style: run pre-commit

Author: henryiii

.pre-commit-config.yaml

@@ -74,7 +74,7 @@ repos:
   - id: mypy
     files: src
     args: []
-    additional_dependencies: [numpy==1.20.1, uhi==0.2.1, types-dataclasses==0.1.3]
+    additional_dependencies: [numpy, uhi, types-dataclasses]
 
 - repo: https://github.com/mgedmin/check-manifest
   rev: "0.46"

examples/cpp/CMakeLists.txt

@@ -0,0 +1,29 @@
+# This file lets you quickly build projects with the exact same boost-histogram
+# settings that the Python bindings use.
+
+cmake_minimum_required(VERSION 3.14...3.20)
+
+project(BOOST_HISTOGRAM_CPP LANGUAGES CXX)
+
+add_library(boost_histogram_cpp IMPORTED INTERFACE)
+
+# these are the boost header-only libraries required by boost::histogram
+target_include_directories(
+  boost_histogram_cpp
+  INTERFACE ../../extern/assert/include
+            ../../extern/config/include
+            ../../extern/core/include
+            ../../extern/histogram/include
+            ../../extern/mp11/include
+            ../../extern/throw_exception/include
+            ../../extern/variant2/include)
+
+target_compile_options(
+  boost_histogram_cpp INTERFACE $<IF:$<CXX_COMPILER_ID:MSVC>,/fp:fast,-funsafe-math-optimizations>)
+
+target_compile_features(boost_histogram_cpp INTERFACE cxx_std_14)
+
+if(PROJECT_NAME STREQUAL CMAKE_PROJECT_NAME)
+  add_executable(simple simple.cpp)
+  target_link_libraries(simple PRIVATE boost_histogram_cpp)
+endif()

examples/cpp/simple.cpp

@@ -0,0 +1,10 @@
+#include <boost/histogram.hpp>
+#include <iostream>
+
+int main() {
+    namespace bh = boost::histogram;
+
+    auto h = bh::make_histogram(bh::axis::category<int>{});
+
+    std::cout << bh::algorithm::sum(h) << std::endl;
+}

tests/test_axis.py

@@ -35,8 +35,10 @@
         (bh.axis.Integer, (1, 2), "", {"circular": True}),
         (bh.axis.IntCategory, ((1, 2, 3),), "", {}),
         (bh.axis.IntCategory, ((1, 2, 3),), "g", {}),
+        (bh.axis.IntCategory, ((),), "g", {}),
         (bh.axis.StrCategory, (tuple("ABC"),), "", {}),
         (bh.axis.StrCategory, (tuple("ABC"),), "g", {}),
+        (bh.axis.StrCategory, ((),), "g", {}),
     ],
 )
 def test_metadata(axis, args, opt, kwargs):

tests/test_histogram.py

@@ -1234,3 +1234,13 @@ def test_np_scalars():
 
     hist /= np.float64(2.0)
     assert hist[bh.loc(7)] == 1.0
+
+
+def test_sum_empty_axis():
+    hist = bh.Histogram(
+        bh.axis.StrCategory("", growth=True),
+        bh.axis.Regular(10, 0, 1),
+        storage=bh.storage.Weight(),
+    )
+    assert hist.sum().value == 0
+    assert "Str" in repr(hist)