a shared empty string

3 files changed, 13 insertions, 0 deletions

diff --git a/vespalib/src/tests/stllike/string_test.cpp b/vespalib/src/tests/stllike/string_test.cpp
index 95846e765f6..de384bce9ad 100644
--- a/vespalib/src/tests/stllike/string_test.cpp
+++ b/vespalib/src/tests/stllike/string_test.cpp
@@ -484,4 +484,9 @@ TEST("test that operator<() works with stringref versus string") {
     EXPECT_FALSE(sb < sb);
 }
 
+TEST("test that empty_string is shared and empty") {
+    EXPECT_TRUE(&empty_string() == &empty_string());
+    EXPECT_EQUAL(empty_string(), "");
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/vespalib/src/vespa/vespalib/stllike/string.cpp b/vespalib/src/vespa/vespalib/stllike/string.cpp
index 67e89d013cc..460bb0d39c6 100644
--- a/vespalib/src/vespa/vespalib/stllike/string.cpp
+++ b/vespalib/src/vespa/vespalib/stllike/string.cpp
@@ -100,4 +100,9 @@ template string operator + (stringref a, const string & b);
 template string operator + (const string & a, const char * b);
 template string operator + (const  char * a, const string & b);
 
+const string &empty_string() {
+    static string empty;
+    return empty;
+}
+
 }
diff --git a/vespalib/src/vespa/vespalib/stllike/string.h b/vespalib/src/vespa/vespalib/stllike/string.h
index 79c9d50b164..2c0bb9a85d3 100644
--- a/vespalib/src/vespa/vespalib/stllike/string.h
+++ b/vespalib/src/vespa/vespalib/stllike/string.h
@@ -675,6 +675,9 @@ inline bool ends_with(stringref text, stringref key) {
     return false;
 }
 
+// returns a reference to a shared empty string
+const string &empty_string();
+
 /**
  * Utility function to format an unsigned integer into a new
  * string instance.