this._ignoreCase = ignoreCase
        this._allowRelativePaths = allowRelativePaths
        this._initCache()
    }

    _initCache () {
        this._ignoreCache = Object.create(null)
        this._testCache = Object.create(null)
    }

    _addPattern (pattern) {
        // #32
        if (pattern && pattern[KEY_IGNORE]) {
            this._rules = this._rules.concat(pattern._rules)
            this._added = true