AK: Add String::join

Author: https://github.com/trflynn89
Commit: https://github.com/SerenityOS/serenity/commit/cccaa94767
Pull-request: https://github.com/SerenityOS/serenity/pull/17206
Reviewed-by: https://github.com/linusg ✅

AK/String.cpp

@@ -10,7 +10,6 @@
 #include <AK/Format.h>
 #include <AK/MemMem.h>
 #include <AK/String.h>
-#include <AK/StringBuilder.h>
 #include <AK/Utf8View.h>
 #include <AK/Vector.h>
 #include <stdlib.h>

AK/String.h

@@ -14,6 +14,7 @@
 #include <AK/Optional.h>
 #include <AK/RefCounted.h>
 #include <AK/Span.h>
+#include <AK/StringBuilder.h>
 #include <AK/StringUtils.h>
 #include <AK/StringView.h>
 #include <AK/Traits.h>
@@ -185,6 +186,14 @@ public:
         return vformatted(fmtstr.view(), variadic_format_parameters);
     }
 
+    template<class SeparatorType, class CollectionType>
+    static ErrorOr<String> join(SeparatorType const& separator, CollectionType const& collection, StringView fmtstr = "{}"sv)
+    {
+        StringBuilder builder;
+        TRY(builder.try_join(separator, collection, fmtstr));
+        return builder.to_string();
+    }
+
     // NOTE: This is primarily interesting to unit tests.
     [[nodiscard]] bool is_short_string() const;
 

Tests/AK/TestString.cpp

@@ -471,3 +471,27 @@ TEST_CASE(repeated)
         return Test::Crash::Failure::DidNotCrash;
     });
 }
+
+TEST_CASE(join)
+{
+    auto string1 = MUST(String::join(',', Vector<i32> {}));
+    EXPECT(string1.is_empty());
+
+    auto string2 = MUST(String::join(',', Array { 1 }));
+    EXPECT_EQ(string2, "1"sv);
+
+    auto string3 = MUST(String::join(':', Array { 1 }, "[{}]"sv));
+    EXPECT_EQ(string3, "[1]"sv);
+
+    auto string4 = MUST(String::join(',', Array { 1, 2, 3 }));
+    EXPECT_EQ(string4, "1,2,3"sv);
+
+    auto string5 = MUST(String::join(',', Array { 1, 2, 3 }, "[{}]"sv));
+    EXPECT_EQ(string5, "[1],[2],[3]"sv);
+
+    auto string6 = MUST(String::join(String::from_utf8_short_string("!!!"sv), Array { "foo"sv, "bar"sv, "baz"sv }));
+    EXPECT_EQ(string6, "foo!!!bar!!!baz"sv);
+
+    auto string7 = MUST(String::join(" - "sv, Array { 1, 16, 256, 4096 }, "[{:#04x}]"sv));
+    EXPECT_EQ(string7, "[0x0001] - [0x0010] - [0x0100] - [0x1000]"sv);
+}