Use vespalib::string in TestAndSetCondition

Avoids some implicit conversions. Add `starts_with` to `vespalib::string`
and `vespalib::stringref` to allow drop-in replacement for Document API code.

2 files changed, 41 insertions, 0 deletions

diff --git a/vespalib/src/tests/stllike/string_test.cpp b/vespalib/src/tests/stllike/string_test.cpp
index de384bce9ad..d60380aa3ab 100644
--- a/vespalib/src/tests/stllike/string_test.cpp
+++ b/vespalib/src/tests/stllike/string_test.cpp
@@ -489,4 +489,23 @@ TEST("test that empty_string is shared and empty") {
     EXPECT_EQUAL(empty_string(), "");
 }
 
+TEST("starts_with has expected semantics for small_string") {
+    vespalib::string a("foobar");
+    EXPECT_TRUE(a.starts_with(""));
+    EXPECT_TRUE(a.starts_with("foo"));
+    EXPECT_TRUE(a.starts_with("foobar"));
+    EXPECT_FALSE(a.starts_with("foobarf"));
+    EXPECT_FALSE(a.starts_with("oobar"));
+}
+
+TEST("starts_with has expected semantics for stringref") {
+    vespalib::string a("foobar");
+    vespalib::stringref ar(a);
+    EXPECT_TRUE(ar.starts_with(""));
+    EXPECT_TRUE(ar.starts_with("foo"));
+    EXPECT_TRUE(ar.starts_with("foobar"));
+    EXPECT_FALSE(ar.starts_with("foobarf"));
+    EXPECT_FALSE(ar.starts_with("oobar"));
+}
+
 TEST_MAIN() { TEST_RUN_ALL(); }
diff --git a/vespalib/src/vespa/vespalib/stllike/string.h b/vespalib/src/vespa/vespalib/stllike/string.h
index 2c0bb9a85d3..2e61d7ef0e9 100644
--- a/vespalib/src/vespa/vespalib/stllike/string.h
+++ b/vespalib/src/vespa/vespalib/stllike/string.h
@@ -111,6 +111,7 @@ public:
         }
         return npos;
     }
+
     /**
      * Find the last occurrence of a substring, starting at e and
      * searching in reverse order.
@@ -126,6 +127,17 @@ public:
         int diff(memcmp(_s, s, std::min(sz, size())));
         return (diff != 0) ? diff : (size() - sz);
     }
+
+    /**
+     * Returns true iff input string is a prefix of this string.
+     */
+    [[nodiscard]] bool starts_with(stringref prefix) const noexcept {
+        if (prefix.size() > size()) {
+            return false;
+        }
+        return (memcmp(data(), prefix.data(), prefix.size()) == 0);
+    }
+
     const char & operator [] (size_t i) const { return _s[i]; }
     operator std::string () const { return std::string(_s, _sz); }
     bool operator  <        (const char * s) const noexcept { return compare(s, strlen(s)) < 0; }
@@ -257,6 +269,16 @@ public:
     }
 
     /**
+     * Returns true iff input string is a prefix of this string.
+     */
+    [[nodiscard]] bool starts_with(stringref prefix) const noexcept {
+        if (prefix.size() > size()) {
+            return false;
+        }
+        return (memcmp(buffer(), prefix.data(), prefix.size()) == 0);
+    }
+
+    /**
      * Find the last occurrence of a substring, starting at e and
      * searching in reverse order.
      *