Add abbreviate(input, max_length, ellipsis)

include/iris/string_algo.hpp

@@ -270,6 +270,49 @@ template<int = 0>
 }
 
 
+// Truncates the tail of the string to `max_length` while replacing the tail with
+// `ellipsis` iff `input.size()` exceeded `max_length`.
+template<class CharT, class TraitsT>
+constexpr void abbreviate(
+    std::basic_string<CharT, TraitsT>& input,
+    std::size_t const max_length,
+    std::type_identity_t<std::basic_string_view<CharT, TraitsT>> ellipsis
+)
+{
+    if (max_length < ellipsis.size()) {
+        throw std::length_error{"ellipsis' length is longer than max_length"};
+    }
+
+    if (input.size() > max_length) {
+        input.replace(max_length - ellipsis.size(), std::basic_string<CharT, TraitsT>::npos, ellipsis);
+    }
+}
+
+template<int = 0>
+constexpr std::string abbreviate_copy(
+    std::string_view input,
+    std::size_t const max_length,
+    std::string_view ellipsis
+)
+{
+    std::string buf(input);
+    iris::abbreviate(buf, max_length, ellipsis);
+    return buf;
+}
+
+template<int = 0>
+constexpr std::u32string abbreviate_copy(
+    std::u32string_view input,
+    std::size_t const max_length,
+    std::u32string_view ellipsis
+)
+{
+    std::u32string buf(input);
+    iris::abbreviate(buf, max_length, ellipsis);
+    return buf;
+}
+
+
 namespace detail {
 
 // Closed range [first, last] of character set

test/string_algo.cpp

@@ -205,6 +205,31 @@ TEST_CASE("string_algo: escape")
 #undef IRIS_TEST_ESCAPE
 }
 
+
+TEST_CASE("string_algo: abbreviate")
+{
+#ifdef _MSC_VER
+    SetConsoleOutputCP(CP_UTF8);
+#endif
+
+    {
+        std::string str;
+        iris::abbreviate(str, 3, "...");
+        CHECK(str == ""sv);
+    }
+
+    CHECK_THROWS_AS(iris::abbreviate_copy("", 2, "..."), std::length_error);
+    CHECK_THROWS_AS(iris::abbreviate_copy("aaaaaa", 2, "..."), std::length_error);
+
+    CHECK(iris::abbreviate_copy("fo", 3, "...") == "fo"sv);
+    CHECK(iris::abbreviate_copy("foo", 3, "...") == "foo"sv);
+    CHECK(iris::abbreviate_copy("foob", 3, "...") == "..."sv);
+
+    CHECK(iris::abbreviate_copy("foo", 4, "...") == "foo"sv);
+    CHECK(iris::abbreviate_copy("foob", 4, "...") == "foob"sv);
+    CHECK(iris::abbreviate_copy("fooba", 4, "...") == "f..."sv);
+}
+
 TEST_CASE("string_algo: ordinary_normalize")
 {
 #ifdef _MSC_VER