Fix strong symbol definitions in Differentiator.h. Add unittests. #335

	name: clang-format

	on:
	pull_request:
	paths:
	- '**.h'
	- '**.cpp'

	concurrency:
	group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
	cancel-in-progress: true

	jobs:
	precheckin:
	runs-on: ubuntu-22.04
	steps:
	- name: Checkout PR branch
	uses: actions/checkout@v3
	with:
	ref: ${{ github.event.pull_request.head.sha }}
	fetch-depth: 0
	- name: Setup Python
	uses: actions/setup-python@v4
	with:
	python-version: 3.7
	- name: Install clang-format
	run: \|
	curl https://apt.llvm.org/llvm-snapshot.gpg.key \| sudo apt-key add -
	echo "deb https://apt.llvm.org/jammy/ llvm-toolchain-jammy-15 main" \| sudo tee -a /etc/apt/sources.list
	sudo apt update
	sudo apt install -y clang-format-15
	- name: Download git-clang-format
	run: \|
	wget https://raw.githubusercontent.com/llvm/llvm-project/main/clang/tools/clang-format/git-clang-format
	chmod +x git-clang-format
	- name: Run git-clang-format
	run: \|
	PR_BASE=$(git rev-list ${{ github.event.pull_request.head.sha }} ^${{ github.event.pull_request.base.sha }} \| tail --lines 1 \| xargs -I {} git rev-parse {}~1)
	echo "running git clang-format against $PR_BASE commit"
	git \
	-c color.ui=always \
	-c diff.wsErrorHighlight=all \
	-c color.diff.whitespace='red reverse' \
	clang-format-15 --diff --binary clang-format-15 --commit $PR_BASE -- demos/ include/ lib/ tools/ \|\| \
	(echo "Please run the following git-clang-format locally to fix the formatting: \n
	git clang-format origin/master -- demos/ include/ lib/ tools/" && exit 1)

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