feat: EQUIV{...} replaced with [...] in the text output of common units

Author: mpusz

docs/users_guide/framework_basics/text_output.md

@@ -304,10 +304,10 @@ std::cout << 1 * rad + 1 * deg << "\n";
 prints:
 
 ```text
-40771 EQUIV{[1/25146 mi], [1/15625 km]}
-108167 EQUIV{[1/50292 mi], [1/57875 nmi]}
-23 EQUIV{[1/5 km/h], [1/18 m/s]}
-183.142 EQUIV{[1/π°], [1/180 rad]}
+40771 [(1/25146 mi), (1/15625 km)]
+108167 [(1/50292 mi), (1/57875 nmi)]
+23 [(1/5 km/h), (1/18 m/s)]
+183.142 [(1/π°), (1/180 rad)]
 ```
 
 Thanks to the above, it might be easier for the user to reason about the magnitude of the resulting

src/core/include/mp-units/framework/unit.h

@@ -802,7 +802,7 @@ template<typename CharT, std::output_iterator<CharT> Out, typename U, typename..
 constexpr Out unit_symbol_impl(Out out, const common_unit<U, Rest...>&, const unit_symbol_formatting& fmt,
                                bool negative_power)
 {
-  constexpr std::string_view prefix("EQUIV{");
+  constexpr std::string_view prefix("[");
   constexpr std::string_view separator(", ");
   auto print_unit = [&]<Unit Arg>(Arg) {
     constexpr auto u = get_common_unit_in(common_unit<U, Rest...>{}, Arg{});
@@ -814,7 +814,7 @@ constexpr Out unit_symbol_impl(Out out, const common_unit<U, Rest...>&, const un
     detail::copy(std::begin(separator), std::end(separator), out);
     print_unit(Arg{});
   });
-  *out++ = '}';
+  *out++ = ']';
   return out;
 }
 

test/static/unit_symbol_test.cpp

@@ -204,13 +204,13 @@ static_assert(unit_symbol(mag<2> / (mag<π> * mag<e>)*one) == "(2 e⁻¹ π⁻¹
 static_assert(unit_symbol<usf{.solidus = always}>(mag<2> / (mag<π> * mag<e>)*one) == "(2/(e π))");
 
 // common units
-static_assert(unit_symbol(get_common_unit(kilo<metre>, mile)) == "EQUIV{(1/25146 mi), (1/15625 km)}");
-static_assert(unit_symbol(get_common_unit(kilo<metre> / hour, metre / second)) == "EQUIV{(1/5 km/h), (1/18 m/s)}");
+static_assert(unit_symbol(get_common_unit(kilo<metre>, mile)) == "[(1/25146 mi), (1/15625 km)]");
+static_assert(unit_symbol(get_common_unit(kilo<metre> / hour, metre / second)) == "[(1/5 km/h), (1/18 m/s)]");
 static_assert(unit_symbol(get_common_unit(kilo<metre> / hour, metre / second) / second) ==
-              "EQUIV{(1/5 km/h), (1/18 m/s)}/s");
+              "[(1/5 km/h), (1/18 m/s)]/s");
 static_assert(unit_symbol(get_common_unit(kilo<metre> / hour, metre / second) * second) ==
-              "EQUIV{(1/5 km/h), (1/18 m/s)} s");
-static_assert(unit_symbol(get_common_unit(radian, degree)) == "EQUIV{(1/π°), (1/180 rad)}");
+              "[(1/5 km/h), (1/18 m/s)] s");
+static_assert(unit_symbol(get_common_unit(radian, degree)) == "[(1/π°), (1/180 rad)]");
 
 // derived units
 static_assert(unit_symbol(one) == "");  // NOLINT(readability-container-size-empty)