Support scaling a unit symbol by a magnitude (#341)

I found this useful in handling some "liters per 100 km" test cases.
aurora-opensource · Dec 2, 2024 · 72c2d06 · 72c2d06
1 parent bb7911f
commit 72c2d06
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diff --git a/au/code/au/unit_symbol.hh b/au/code/au/unit_symbol.hh
@@ -30,7 +30,8 @@ namespace au {
 template <typename Unit>
 struct SymbolFor : detail::MakesQuantityFromNumber<SymbolFor, Unit>,
                    detail::ScalesQuantity<SymbolFor, Unit>,
-                   detail::ComposesWith<SymbolFor, Unit, SymbolFor, SymbolFor> {};
+                   detail::ComposesWith<SymbolFor, Unit, SymbolFor, SymbolFor>,
+                   detail::CanScaleByMagnitude<SymbolFor, Unit> {};
 
 //
 // Create a unit symbol using the more fluent APIs that unit slots make possible.  For example:

diff --git a/au/code/au/unit_symbol_test.cc b/au/code/au/unit_symbol_test.cc
@@ -43,4 +43,12 @@ TEST(SymbolFor, ScalesUnitsOfExistingQuantity) {
 
 TEST(SymbolFor, CompatibleWithUnitSlot) { EXPECT_THAT(meters(35u).in(m), SameTypeAndValue(35u)); }
 
+TEST(SymbolFor, CanScaleByMagnitude) {
+    // Yes, the identifier name is a little awkward for these symbols for anonymous scaled units.
+    // But it's still important to have this functionality.
+    constexpr auto u100_m = mag<100>() * m;
+
+    EXPECT_THAT(3.5f / u100_m, SameTypeAndValue(inverse(meters * mag<100>())(3.5f)));
+}
+
 }  // namespace au