I have no luck installing Swoole via home brew or pecl. So I installed it manually and works. So here my step:
Make sure you php installed on your osx
php -v
phpize -v
Go to temporary folder
cd /tmp/
Download the source code
wget "https://github.com/swoole/swoole-src/archive/v4.0.3.tar.gz" -O swoole.tar.gz
Extract the file
tar xvzf swoole.tar.gz
Go to source folder
cd swoole-src-4.0.3/
Prepare the build environment for a PHP extension
phpize
Add configuration paramaters as needed
./configure
Run make. This will take some time a successful result of make is module/swoole.so
make
create Swoole extension directory
mkdir -p /usr/local/opt/php71-swoole/
install the swoole into the PHP extensions directory
cp modules/swoole.so /usr/local/opt/php71-swoole/
Create config file for Swoole
touch /usr/local/etc/php/7.1/conf.d/ext-swoole.ini
echo "extension=/usr/local/opt/php71-swoole/swoole.so" > /usr/local/etc/php/7.1/conf.d/ext-swoole.ini
check if the swoole extension has been enabled php -m | grep swoole
If succeed, it will send you output something like "swoole"
PS: I run PHP 7.1 and Swoole 4.0.3. Adjust it with your own version.