[library/cpp/logger] Support meta flags with TLogElement

Support opportunity to use TMetaFlags with TLogElement.

**Use example:**
`Log().With("Property", "Value").With("Code", "Code") << LogMessage`

Such interface allows to not parse required by TLogBackend  properties from raw string.

1 files changed, 17 insertions, 9 deletions

diff --git a/library/cpp/logger/element.h b/library/cpp/logger/element.h
index fc9bff851f..9ba27ab67e 100644
--- a/library/cpp/logger/element.h
+++ b/library/cpp/logger/element.h
@@ -1,18 +1,20 @@
 #pragma once
 
 #include "priority.h"
+#include "record.h"
 
+
+#include <util/string/cast.h>
 #include <util/stream/tempbuf.h>
 
+
 class TLog;
 
-/*
- * better do not use directly
- */
+/// @warning Better don't use directly.
 class TLogElement: public TTempBufOutput {
 public:
-    TLogElement(const TLog* parent);
-    TLogElement(const TLog* parent, ELogPriority priority);
+    explicit TLogElement(const TLog* parent);
+    explicit TLogElement(const TLog* parent, ELogPriority priority);
 
     TLogElement(TLogElement&&) noexcept = default;
     TLogElement& operator=(TLogElement&&) noexcept = default;
@@ -26,15 +28,20 @@ public:
         return *this;
     }
 
-    /*
-         * for pretty usage: logger << TLOG_ERROR << "Error description";
-         */
+    /// @note For pretty usage: logger << TLOG_ERROR << "Error description";
     inline TLogElement& operator<<(ELogPriority priority) {
         Flush();
         Priority_ = priority;
         return *this;
     }
 
+    template<typename T>
+    TLogElement& With(const TStringBuf key, const T value) {
+        Context_.emplace_back(key, ToString(value));
+
+        return *this;
+    }
+
     ELogPriority Priority() const noexcept {
         return Priority_;
     }
@@ -43,6 +50,7 @@ protected:
     void DoFlush() override;
 
 protected:
-    const TLog* Parent_;
+    const TLog* Parent_ = nullptr;
     ELogPriority Priority_;
+    TLogRecord::TMetaFlags Context_;
 };