SearchIssue.swift

private var lastScheduledWord: dispatch_cancelable_block_t?
private var lastRequest: NSURLSessionTask?

func searchRepository(keyword: String) {
    cancel_block(lastScheduledWord)
    
    lastRequest?.cancel()
    lastRequest = nil
    
    lastScheduledWord = dispatch_after_delay(0.5) {
        lastRequest = findRepository(keyword, success: { repository in
            findIssues(repository)
            }, failure: { error in
                    displayError(error)
                }
        })
    }
}