Conventions

This section provides some information about some of the abstractions and development approaches we use to solve problems common to many parts of the C++ project.

File Naming

C++ source and header files should use underscores for word separation, not hyphens. Compiled executables, however, will automatically use hyphens (such that e.g. src/arrow/scalar_test.cc will be compiled into arrow-scalar-test).

C++ header files use the .h extension. Any header file name not containing internal is considered to be a public header, and will be automatically installed by the build.

Comments and Docstrings

Regular comments start with //.

Doxygen docstrings start with ///, and Doxygen directives start with \, like this:

/// \brief Allocate a fixed size mutable buffer from a memory pool, zero its padding.
///
/// \param[in] size size of buffer to allocate
/// \param[in] pool a memory pool
ARROW_EXPORT
Result<std::unique_ptr<Buffer>> AllocateBuffer(const int64_t size,
                                               MemoryPool* pool = NULLPTR);

The summary line of a docstring uses the infinitive, not the indicative (for example, “Allocate a buffer” rather than “Allocates a buffer”).

Memory Pools

We provide a default memory pool with arrow::default_memory_pool().

Error Handling and Exceptions

For error handling, we return arrow::Status values instead of throwing C++ exceptions. Since the Arrow C++ libraries are intended to be useful as a component in larger C++ projects, using Status objects can help with good code hygiene by making explicit when a function is expected to be able to fail.

A more recent option is to return a arrow::Result<T> object that can represent either a successful result with a T value, or an error result with a Status value.

For expressing internal invariants and “cannot fail” errors, we use DCHECK macros defined in arrow/util/logging.h. These checks are disabled in release builds and are intended to catch internal development errors, particularly when refactoring. These macros are not to be included in any public header files.

Since we do not use exceptions, we avoid doing expensive work in object constructors. Objects that are expensive to construct may often have private constructors, with public static factory methods that return Status or Result<T>.

There are a number of object constructors, like arrow::Schema and arrow::RecordBatch where larger STL container objects like std::vector may be created. While it is possible for std::bad_alloc to be thrown in these constructors, the circumstances where they would are somewhat esoteric, and it is likely that an application would have encountered other more serious problems prior to having std::bad_alloc thrown in a constructor.

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