Function composer_cache_dir 

pub fn composer_cache_dir() -> PathBuf

Factory::getCacheDir: COMPOSER_CACHE_DIR; else $COMPOSER_HOME/cache if COMPOSER_HOME is set; Windows -> %LOCALAPPDATA%/Composer (else <home>/cache); Darwin -> ~/Library/Caches/composer; ~/.composer/cache if it exists; XDG -> $XDG_CACHE_HOME/composer; else <home>/cache.