Hello C++ Native Extension

A minimal Daft native extension written in pure C++ using the Apache Arrow C++ library.

This is the C++ counterpart of the hello Rust example. It implements a single greet_cpp scalar function that prepends "Hello, " to every string in a column.

Prerequisites

CMake >= 3.20
A C++17 compiler
Apache Arrow C++ (with headers)

Install Arrow C++

macOS (Homebrew):

bash

brew install apache-arrow

Ubuntu / Debian:

bash

sudo apt install -y libarrow-dev

Conda:

bash

conda install -c conda-forge arrow-cpp

Development

Build the shared library

bash

cmake -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
cmake --build build

The CMAKE_EXPORT_COMPILE_COMMANDS flag generates build/compile_commands.json for clangd / LSP support. Symlink it to the project root if your editor needs it:

bash

ln -sf build/compile_commands.json .

Install as a Python package

bash

uv pip install -e .

This uses scikit-build-core to build the C++ library and install it into the Python package.

Run tests

bash

pytest -v tests/

Usage

python

import daft
import hello_cpp
from hello_cpp import greet
from daft import col
from daft.session import Session

sess = Session()
sess.load_extension(hello_cpp)

df = daft.from_pydict({"name": ["John", "Paul", "George", None]})

with sess:
    df.select(greet(col("name"))).show()

# ╭──────────────────╮
# │ greet_cpp         │
# │ ---               │
# │ Utf8              │
# ╞══════════════════╡
# │ Hello, John!      │
# ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤
# │ Hello, Paul!      │
# ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤
# │ Hello, George!    │
# ├╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌┤
# │ None              │
# ╰──────────────────╯