Introduce TLazyMultiValueFormatter

3 files changed, 81 insertions, 0 deletions

diff --git a/library/cpp/yt/string/format-inl.h b/library/cpp/yt/string/format-inl.h
index 2eb42cfb99..cb27961d3b 100644
--- a/library/cpp/yt/string/format-inl.h
+++ b/library/cpp/yt/string/format-inl.h
@@ -633,6 +633,35 @@ void FormatImpl(
 
 ////////////////////////////////////////////////////////////////////////////////
 
+template <class... TArgs>
+TLazyMultiValueFormatter<TArgs...>::TLazyMultiValueFormatter(
+    TStringBuf format,
+    TArgs&&... args)
+    : Format_(format)
+    , Args_(std::forward<TArgs>(args)...)
+{ }
+
+template <class... TArgs>
+void FormatValue(
+    TStringBuilderBase* builder,
+    const TLazyMultiValueFormatter<TArgs...>& value,
+    TStringBuf /*format*/)
+{
+    std::apply(
+        [&] <class... TInnerArgs> (TInnerArgs&&... args) {
+            builder->AppendFormat(value.Format_, std::forward<TInnerArgs>(args)...);
+        },
+        value.Args_);
+}
+
+template <class... TArgs>
+auto MakeLazyMultiValueFormatter(TStringBuf format, TArgs&&... args)
+{
+    return TLazyMultiValueFormatter<TArgs...>(format, std::forward<TArgs>(args)...);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
 template <class T>
 struct TFormatTraits
 {
diff --git a/library/cpp/yt/string/format.h b/library/cpp/yt/string/format.h
index 9708fe5906..8e0d5f82e5 100644
--- a/library/cpp/yt/string/format.h
+++ b/library/cpp/yt/string/format.h
@@ -107,6 +107,45 @@ TFormatterWrapper<TFormatter> MakeFormatterWrapper(
 
 ////////////////////////////////////////////////////////////////////////////////
 
+template <class... TArgs>
+class TLazyMultiValueFormatter;
+
+template <class... TArgs>
+void FormatValue(
+    TStringBuilderBase* builder,
+    const TLazyMultiValueFormatter<TArgs...>& value,
+    TStringBuf /*format*/);
+
+//! A wrapper for a bunch of values that formats them lazily on demand.
+/*!
+ *  The intended use of this class is when you need to use the same formatted string
+ *  in several places in the function (e.g. log message tags) and want both to avoid
+ *  code duplication and premature formatting of the values until necessary.
+ *
+ *  NB: lvalues are captured by reference without lifetime extension.
+ */
+template <class... TArgs>
+class TLazyMultiValueFormatter
+    : private TNonCopyable
+{
+public:
+    TLazyMultiValueFormatter(TStringBuf format, TArgs&&... args);
+
+    friend void FormatValue<>(
+        TStringBuilderBase* builder,
+        const TLazyMultiValueFormatter& value,
+        TStringBuf /*format*/);
+
+private:
+    const TStringBuf Format_;
+    const std::tuple<TArgs...> Args_;
+};
+
+template <class ... Args>
+auto MakeLazyMultiValueFormatter(TStringBuf format, Args&&... args);
+
+////////////////////////////////////////////////////////////////////////////////
+
 } // namespace NYT
 
 #define FORMAT_INL_H_
diff --git a/library/cpp/yt/string/unittests/format_ut.cpp b/library/cpp/yt/string/unittests/format_ut.cpp
index 89aa01766f..e8965ee947 100644
--- a/library/cpp/yt/string/unittests/format_ut.cpp
+++ b/library/cpp/yt/string/unittests/format_ut.cpp
@@ -183,6 +183,19 @@ TEST(TFormatTest, Pointers)
     }
 }
 
+TEST(TFormatTest, LazyMultiValueFormatter)
+{
+    int i = 1;
+    TString s = "hello";
+    std::vector<int> range{1, 2, 3};
+    auto lazyFormatter = MakeLazyMultiValueFormatter(
+        "int: %v, string: %v, range: %v",
+        i,
+        s,
+        MakeFormattableView(range, TDefaultFormatter{}));
+    EXPECT_EQ("int: 1, string: hello, range: [1, 2, 3]", Format("%v", lazyFormatter));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 } // namespace