translation unit

在進入unnamed namespace前，必須先有translation unit的概念。以下段落摘自What is a “translation unit” in C++：

A translation unit is the basic unit of compilation in C++. 
It consists of the contents of a single source file, 
plus the contents of any header files directly or indirectly included by it, 
minus those lines that were ignored using conditional preprocessing statements.

A single translation unit can be compiled into an object file, 
library, or executable program.

The notion of a translation unit is most often mentioned in the 
contexts of the One Definition Rule, and templates.

一個translation unit由"一個"source file，及其引入的數個header files，減去那些因預處理而被忽略的代碼。

一個translation unit會被編譯成一個object file，library，或是可執行檔。

anonymous namespace(unnamed namespace)

unnamed namespace的作用是讓它所包含的變數或函數只能被其所屬的translation unit所見。

在C語言裡，我們用static修飾字來修飾函數來達到同樣的功能，但是使用unnamed namespace是比較被鼓勵的，詳見：Superiority of unnamed namespace over static?。

以下是在TensorRT/samples/common/logging.h中定義的unnamed namespace：

namespace
{

//...

inline LogStreamConsumer LOG_INFO(const Logger& logger)
{
    return LogStreamConsumer(logger.getReportableSeverity(), Severity::kINFO);
}

//...

} // anonymous namespace