我想提出一个让我陷入困境的主题，并提出了一个关于 齐::符号。
这一切都始于我查看新的野兽图书馆并阅读 a tutorial example
它以一个从 http 路径猜测 mime 类型的函数开始 扩展。我开始仔细观察，看到了这个:
auto const ext = [&path]
{
auto const pos = path.rfind(".");
if(pos == boost::beast::string_view::npos)
return boost::beast::string_view{};
return path.substr(pos);
}();
我花了一段时间才弄清楚这是一个 IIFE在 C++ 风格中，用于初始化 ext，同时声明它为常量。
无论如何，我开始测试这是否会产生任何性能差异 将证明可怕的可读性与直接实现相比是合理的。
这样做我开始怀疑这在 齐::符号。所以我想出了两个替代实现:
#include <boost/smart_ptr/scoped_array.hpp>
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics/stats.hpp>
#include <boost/accumulators/statistics/mean.hpp>
#include <boost/accumulators/statistics/moment.hpp>
#include <boost/chrono.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/qi_parse.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/fusion/include/vector.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/algorithm/string.hpp>
#include <boost/assign.hpp>
#include <iostream>
#include <string>
#include <vector>
#include <random>
using namespace boost::accumulators;
typedef boost::chrono::duration<long long, boost::micro> microseconds;
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace ascii = qi::ascii;
namespace phx = boost::phoenix;
const std::map<const std::string, const std::string> mime_exts = {
{ ".htm", "text/html" },
{ ".html", "text/html" },
{ ".php", "text/html" },
{ ".css", "text/css" },
{ ".js", "application/javascript" },
{ ".json", "application/json" },
{ ".xml", "application/xml" },
{ ".swf", "application/x-shockwave-flash" },
{ ".flv", "video/x-flv" },
{ ".png", "image/png" },
{ ".jpe", "image/jpeg" },
{ ".jpeg", "image/jpeg" },
{ ".jpg", "image/jpeg" },
{ ".gif", "image/gif" },
{ ".bmp", "image/bmp" },
{ ".ico", "image/vnd.microsoft.icon" },
{ ".tif", "image/tiff" },
{ ".tiff", "image/tiff" },
{ ".svg", "image/svg+xml"},
{ ".svgz", "image/svg+xml"}
};
const char *mime_literals[] = {
"text/html",
"text/css",
"text/plain",
"application/javascript",
"application/json",
"application/xml",
"application/x-shockwave-flash",
"video/x-flv",
"image/png",
"image/jpeg",
"image/gif",
"image/bmp",
"image/vnd.microsoft.icon",
"image/tiff",
"image/svg+xml"
};
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, unsigned int()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start, "mimetype_matching_parser") {
m_mime_extensions.add
(".htm", 0)
(".html", 0)
(".php", 0)
(".css", 1)
(".txt", 2)
(".js", 3)
(".json", 4)
(".xml", 5)
(".swf", 6)
(".flv", 7)
(".png", 8)
(".jpe", 9)
(".jpeg", 9)
(".jpg", 9)
(".gif", 10)
(".bmp", 11)
(".ico", 12)
(".tiff", 13)
(".tif", 13)
(".svg", 14)
(".svgz", 14)
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, unsigned int> m_mime_extensions;
qi::rule<Iterator, unsigned int()> m_start;
};
std::string mime_extension(const std::string &n_path) {
// First locate the extension itself
const std::size_t last_dot = n_path.rfind(".");
if (last_dot == std::string::npos) {
return "application/text";
}
// and now pipe the extension into a qi symbols parser.
// I don't know if this is any faster than a more trivial algorithm::ends_with
// approach but I guess it won't be any slower
const mimetype_matching_parser<std::string::const_iterator> p;
unsigned int result;
std::string::const_iterator begin = n_path.begin() + last_dot;
const std::string::const_iterator end = n_path.end();
try {
if (qi::parse(begin, end, p, result) && (begin == end)) {
return mime_literals[result];
} else {
return "application/text";
}
} catch (const std::exception &) { // asio throws on invalid parse
return "application/text";
}
}
std::string mime_extension2(const std::string &n_path) {
using boost::algorithm::iequals;
auto const ext = [&n_path] {
auto const pos = n_path.rfind(".");
if (pos == std::string::npos)
return std::string{};
return n_path.substr(pos);
}();
// const std::size_t pos = n_path.rfind(".");
// if (pos == std::string::npos) {
// return std::string{};
// }
// const std::string ext = n_path.substr(pos);
if (iequals(ext, ".htm")) return "text/html";
if (iequals(ext, ".html")) return "text/html";
if (iequals(ext, ".php")) return "text/html";
if (iequals(ext, ".css")) return "text/css";
if (iequals(ext, ".txt")) return "text/plain";
if (iequals(ext, ".js")) return "application/javascript";
if (iequals(ext, ".json")) return "application/json";
if (iequals(ext, ".xml")) return "application/xml";
if (iequals(ext, ".swf")) return "application/x-shockwave-flash";
if (iequals(ext, ".flv")) return "video/x-flv";
if (iequals(ext, ".png")) return "image/png";
if (iequals(ext, ".jpe")) return "image/jpeg";
if (iequals(ext, ".jpeg")) return "image/jpeg";
if (iequals(ext, ".jpg")) return "image/jpeg";
if (iequals(ext, ".gif")) return "image/gif";
if (iequals(ext, ".bmp")) return "image/bmp";
if (iequals(ext, ".ico")) return "image/vnd.microsoft.icon";
if (iequals(ext, ".tiff")) return "image/tiff";
if (iequals(ext, ".tif")) return "image/tiff";
if (iequals(ext, ".svg")) return "image/svg+xml";
if (iequals(ext, ".svgz")) return "image/svg+xml";
return "application/text";
}
std::string mime_extension3(const std::string &n_path) {
using boost::algorithm::iequals;
auto ext = [&n_path] {
auto const pos = n_path.rfind(".");
if (pos == std::string::npos) {
return std::string{};
} else {
return n_path.substr(pos);
}
}();
boost::algorithm::to_lower(ext);
const std::map<const std::string, const std::string>::const_iterator i = mime_exts.find(ext);
if (i != mime_exts.cend()) {
return i->second;
} else {
return "application/text";
}
}
const std::string samples[] = {
"test.txt",
"test.html",
"longer/test.tiff",
"www.webSite.de/ico.ico",
"www.websIte.de/longEr/path/ico.bmp",
"www.TEST.com/longer/path/ico.svg",
"googlecom/shoRT/path/index.HTM",
"googlecom/bild.jpg",
"WWW.FLASH.COM/app.swf",
"WWW.FLASH.COM/BILD.GIF"
};
int test_qi_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int test_lambda_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension2(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int test_map_impl() {
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<> dis(0, 10);
const std::string sample = samples[dis(gen)];
const std::string result = mime_extension3(sample);
int ret = dis(gen);
for (const char &c : result) { ret += c; }
return ret;
}
int main(int argc, char **argv) {
const unsigned int loops = 100000;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_qi;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_lambda;
accumulator_set<boost::chrono::high_resolution_clock::duration, features<tag::mean> > times_map;
std::cout << "Measure execution times for " << loops << " lambda runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_lambda_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_lambda(end - start);
}
std::cout << "Measure execution times for " << loops << " qi runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_qi_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_qi(end - start);
}
std::cout << "Measure execution times for " << loops << " map runs" << std::endl;
for (unsigned int i = 0; i < loops; i++) {
boost::chrono::high_resolution_clock::time_point start = boost::chrono::high_resolution_clock::now();
test_map_impl();
boost::chrono::high_resolution_clock::time_point end = boost::chrono::high_resolution_clock::now();
times_map(end - start);
}
std::cout << "Lambda runs took " << mean(times_lambda) << std::endl;
std::cout << "Qi runs took " << mean(times_qi) << std::endl;
std::cout << "Map runs took " << mean(times_map) << std::endl;
return EXIT_SUCCESS;
}
令我惊讶的是，lambda 确实很重要(一点点)。让我吃惊的是 更重要的是，qi 的实现速度要慢得多。
Measure execution times for 100000 lambda runs
Measure execution times for 100000 qi runs
Measure execution times for 100000 map runs
Lambda runs took 12443 nanoseconds
Qi runs took 15311 nanoseconds
Map runs took 10466 nanoseconds
首先，我使用的是这样的符号
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, std::string()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start,
"mimetype_matching_parser") {
m_mime_extensions.add
(".htm", "text/html")
(".html", "text/html")
(".php", "text/html")
(".css", "text/css")
(".svg", "whatever...")
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, std::string> m_mime_extensions;
qi::rule<Iterator, std::string()> m_start;
};
直接返回字符串作为属性。有同事指出 这是一个额外的 std::string 拷贝所以我改变了它所以它只返回一个索引到 静态字符数组:
const char *mime_literals[] = {
"text/html",
"text/css",
"text/plain",
// ... and so forth
};
template <typename Iterator>
struct mimetype_matching_parser : qi::grammar<Iterator, unsigned int()> {
mimetype_matching_parser() : mimetype_matching_parser::base_type(m_start, "mimetype_matching_parser")
{
m_mime_extensions.add
(".htm",0)
(".html",0)
(".php",0)
(".css",1)
(".svg",... etc.
;
using qi::no_case;
m_start %= no_case[m_mime_extensions] >> qi::eoi;
}
qi::symbols<char, unsigned int> m_mime_extensions;
qi::rule<Iterator, unsigned int()> m_start;
};
这有点快，但真的不值得一提。
在我的笔记本电脑上，在 Release模式下，我得到: - Beast Tutorial (Lambda) 实现平均每次运行 6200 纳秒。 - Qi 实现平均耗时约 7100 纳秒。
现在，这将是我的第一个问题:这是为什么？
“野兽”实现让我印象深刻，因为它经历了所有 子字符串，每次都调用 iequals，同时它能够缓存 小写。
我认为 qi 肯定会对我添加到 符号解析器。但它看起来不像。
所以我想出了我自己的，也是微不足道的实现，并使用静态 map 临时缓存的小写字母(请参阅附加源中的 impl3)。
测试结果:
Sooo，我想问题是为什么？
我是否以某种方式滥用了 qi::symbols？它实际上进行了二进制搜索但是
性能在其他地方丢失了吗？
斯蒂芬¹
(我在 Windows MSVC14 64 位上，boost 1.66)
(¹ 这个问题是从 Spirit General 邮件列表中转述的，它发布于 20180112T14:15CET；online archives 似乎很遗憾地坏掉了)
最佳答案
在 12-01-18 14:15，Stephan Menzel 写道:
So I came up with two different implementations. Please find the source attached.
我看过了。首先进行一些粗略的观察:
您是在比较苹果和梨，因为 Beast 使用零拷贝字符串 View ，而 Qi 没有。
此外，样本选择调用 UB 因为 uniform_int_distribution(0,10)超出样本数组的范围(应为 (0, 9) )。
最后， map 方法没有 .txt 扩展名的映射。
有了这些，我将测试程序简化/结构化为以下内容:
在我的系统上打印以下内容:
Lambda runs took 2319 nanoseconds
Qi runs took 2841 nanoseconds
Map runs took 193 nanoseconds
现在，最大的罪魁祸首是(显然？)您每次都在通过循环构建语法(编译规则)。当然，没有必要。删除产量:
Lambda runs took 2676 nanoseconds
Qi runs took 98 nanoseconds
Map runs took 189 nanoseconds
这已经更快了，即使您在没有实际需要时仍在复制字符串。使用上面链接的答案的灵感，我可能会这样写:
#include <boost/spirit/include/qi.hpp>
namespace qi_impl {
namespace qi = boost::spirit::qi;
struct mimetype_symbols_type : qi::symbols<char, char const*> {
mimetype_symbols_type() {
auto rev = [](string_view s) -> std::string { return { s.rbegin(), s.rend() }; };
this->add
(rev(".htm"), "text/html")
(rev(".html"), "text/html")
(rev(".php"), "text/html")
(rev(".css"), "text/css")
(rev(".txt"), "text/plain")
(rev(".js"), "application/javascript")
(rev(".json"), "application/json")
(rev(".xml"), "application/xml")
(rev(".swf"), "application/x-shockwave-flash")
(rev(".flv"), "video/x-flv")
(rev(".png"), "image/png")
(rev(".jpe"), "image/jpeg")
(rev(".jpeg"), "image/jpeg")
(rev(".jpg"), "image/jpeg")
(rev(".gif"), "image/gif")
(rev(".bmp"), "image/bmp")
(rev(".ico"), "image/vnd.microsoft.icon")
(rev(".tiff"), "image/tiff")
(rev(".tif"), "image/tiff")
(rev(".svg"), "image/svg+xml")
(rev(".svgz"), "image/svg+xml")
;
}
} static const mime_symbols;
char const* using_spirit(const string_view &n_path) {
char const* result = "application/text";
qi::parse(n_path.crbegin(), n_path.crend(), qi::no_case[mime_symbols], result);
return result;
}
}
不再需要首先寻找“最后一个点”，也不需要“检查匹配项是否在末尾”，您可以直接从符号中获取值。您可以自由分配给 string_view或 std::string随心所欲。
自始至终使用 string_views(支持/显示 std::string_view 和 boost::string_view)。
Note also this shows a custom comparator being used on the
map<>approach, just to prove that indeed there's a benefit from knowing that the map keys are all lower-case. (It's not, in fact, because it "cached the lowercase" since it's only used once!)
#include <boost/chrono.hpp>
#include <string>
#ifdef BOOST_STRING_VIEW
#include <boost/utility/string_view.hpp>
using string_view = boost::string_view;
#else
#include <string_view>
using string_view = std::string_view;
#endif
static auto constexpr npos = string_view::npos;
#include <boost/spirit/include/qi.hpp>
namespace qi_impl {
namespace qi = boost::spirit::qi;
struct mimetype_symbols_type : qi::symbols<char, char const*> {
mimetype_symbols_type() {
auto rev = [](string_view s) -> std::string { return { s.rbegin(), s.rend() }; };
this->add
(rev(".htm"), "text/html")
(rev(".html"), "text/html")
(rev(".php"), "text/html")
(rev(".css"), "text/css")
(rev(".txt"), "text/plain")
(rev(".js"), "application/javascript")
(rev(".json"), "application/json")
(rev(".xml"), "application/xml")
(rev(".swf"), "application/x-shockwave-flash")
(rev(".flv"), "video/x-flv")
(rev(".png"), "image/png")
(rev(".jpe"), "image/jpeg")
(rev(".jpeg"), "image/jpeg")
(rev(".jpg"), "image/jpeg")
(rev(".gif"), "image/gif")
(rev(".bmp"), "image/bmp")
(rev(".ico"), "image/vnd.microsoft.icon")
(rev(".tiff"), "image/tiff")
(rev(".tif"), "image/tiff")
(rev(".svg"), "image/svg+xml")
(rev(".svgz"), "image/svg+xml")
;
}
} static const mime_symbols;
char const* using_spirit(const string_view &n_path) {
char const* result = "application/text";
qi::parse(n_path.crbegin(), n_path.crend(), qi::no_case[mime_symbols], result);
return result;
}
}
#include <boost/algorithm/string.hpp>
namespace impl {
string_view using_iequals(const string_view &n_path) {
using boost::algorithm::iequals;
auto const ext = [&n_path] {
auto pos = n_path.rfind(".");
return pos != npos? n_path.substr(pos) : string_view {};
}();
if (iequals(ext, ".htm")) return "text/html";
if (iequals(ext, ".html")) return "text/html";
if (iequals(ext, ".php")) return "text/html";
if (iequals(ext, ".css")) return "text/css";
if (iequals(ext, ".txt")) return "text/plain";
if (iequals(ext, ".js")) return "application/javascript";
if (iequals(ext, ".json")) return "application/json";
if (iequals(ext, ".xml")) return "application/xml";
if (iequals(ext, ".swf")) return "application/x-shockwave-flash";
if (iequals(ext, ".flv")) return "video/x-flv";
if (iequals(ext, ".png")) return "image/png";
if (iequals(ext, ".jpe")) return "image/jpeg";
if (iequals(ext, ".jpeg")) return "image/jpeg";
if (iequals(ext, ".jpg")) return "image/jpeg";
if (iequals(ext, ".gif")) return "image/gif";
if (iequals(ext, ".bmp")) return "image/bmp";
if (iequals(ext, ".ico")) return "image/vnd.microsoft.icon";
if (iequals(ext, ".tiff")) return "image/tiff";
if (iequals(ext, ".tif")) return "image/tiff";
if (iequals(ext, ".svg")) return "image/svg+xml";
if (iequals(ext, ".svgz")) return "image/svg+xml";
return "application/text";
}
}
#include <boost/algorithm/string.hpp>
#include <map>
namespace impl {
struct CiCmp {
template <typename R1, typename R2>
bool operator()(R1 const& a, R2 const& b) const {
return boost::algorithm::ilexicographical_compare(a, b);
}
};
static const std::map<string_view, string_view, CiCmp> s_mime_exts_map {
{ ".txt", "text/plain" },
{ ".htm", "text/html" },
{ ".html", "text/html" },
{ ".php", "text/html" },
{ ".css", "text/css" },
{ ".js", "application/javascript" },
{ ".json", "application/json" },
{ ".xml", "application/xml" },
{ ".swf", "application/x-shockwave-flash" },
{ ".flv", "video/x-flv" },
{ ".png", "image/png" },
{ ".jpe", "image/jpeg" },
{ ".jpeg", "image/jpeg" },
{ ".jpg", "image/jpeg" },
{ ".gif", "image/gif" },
{ ".bmp", "image/bmp" },
{ ".ico", "image/vnd.microsoft.icon" },
{ ".tif", "image/tiff" },
{ ".tiff", "image/tiff" },
{ ".svg", "image/svg+xml"},
{ ".svgz", "image/svg+xml"},
};
string_view using_map(const string_view& n_path) {
auto const ext = [](string_view n_path) {
auto pos = n_path.rfind(".");
return pos != npos? n_path.substr(pos) : string_view {};
};
auto i = s_mime_exts_map.find(ext(n_path));
if (i != s_mime_exts_map.cend()) {
return i->second;
} else {
return "application/text";
}
}
}
#include <random>
namespace samples {
static string_view const s_samples[] = {
"test.txt",
"test.html",
"longer/test.tiff",
"www.webSite.de/ico.ico",
"www.websIte.de/longEr/path/ico.bmp",
"www.TEST.com/longer/path/ico.svg",
"googlecom/shoRT/path/index.HTM",
"googlecom/bild.jpg",
"WWW.FLASH.COM/app.swf",
"WWW.FLASH.COM/BILD.GIF"
};
std::mt19937 s_random_generator(std::random_device{}());
std::uniform_int_distribution<> s_dis(0, boost::size(s_samples) - 1);
string_view random_sample() {
return s_samples[s_dis(s_random_generator)];
}
}
#include <boost/functional/hash.hpp>
#include <iostream>
template <typename F>
int generic_test(F f) {
auto sample = samples::random_sample();
string_view result = f(sample);
//std::cout << "DEBUG " << sample << " -> " << result << "\n";
return boost::hash_range(result.begin(), result.end());
}
#include <boost/serialization/array_wrapper.hpp> // missing include in boost version on coliru
#include <boost/accumulators/accumulators.hpp>
#include <boost/accumulators/statistics.hpp>
template <typename F>
auto benchmark(F f) {
using C = boost::chrono::high_resolution_clock;
using duration = C::duration;
const unsigned int loops = 100000;
namespace ba = boost::accumulators;
ba::accumulator_set<duration, ba::features<ba::tag::mean>> times;
for (unsigned int i = 0; i < loops; i++) {
auto start = C::now();
generic_test(f);
times(C::now() - start);
}
return ba::mean(times);
}
int main() {
std::cout << std::unitbuf;
std::cout << "Lambda runs took " << benchmark(impl::using_iequals) << std::endl;
std::cout << "Qi runs took " << benchmark(qi_impl::using_spirit) << std::endl;
std::cout << "Map runs took " << benchmark(impl::using_map) << std::endl;
}
打印
Lambda runs took 2470 nanoseconds
Qi runs took 119 nanoseconds
Map runs took 2239 nanoseconds // see Note above
关于c++ - Qi Symbols 性能慢？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48235133/
我的瘦服务器配置了nginx，我的ROR应用程序正在它们上运行。在我发布代码更新时运行thinrestart会给我的应用程序带来一些停机时间。我试图弄清楚如何优雅地重启正在运行的Thin实例，但找不到好的解决方案。有没有人能做到这一点？ 最佳答案 #Restartjustthethinserverdescribedbythatconfigsudothin-C/etc/thin/mysite.ymlrestartNginx将继续运行并代理请求。如果您将Nginx设置为使用多个上游服务器，例如server{listen80;server
如何将send与+=一起使用？a=20;a.send"+=",10undefinedmethod`+='for20:Fixnuma=20;a+=10=>30 最佳答案 恐怕你不能。+=不是方法，而是语法糖。参见http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html它说Incommonwithmanyotherlanguages,Rubyhasasyntacticshortcut:a=a+2maybewrittenasa+=2.你能做的最好的事情是:
我对如何计算通过{%assignvar=0%}赋值的变量加一完全感到困惑。这应该是最简单的任务。到目前为止，这是我尝试过的:{%assignamount=0%}{%forvariantinproduct.variants%}{%assignamount=amount+1%}{%endfor%}Amount:{{amount}}结果总是0。也许我忽略了一些明显的东西。也许有更好的方法。我想要存档的只是获取运行的迭代次数。 最佳答案 因为{{incrementamount}}将输出您的变量值并且不会影响{%assign%}定义的变量，我
我有一个数组数组，想将元素附加到子数组。+=做我想做的，但我想了解为什么push不做。我期望的行为(并与+=一起工作):b=Array.new(3,[])b[0]+=["apple"]b[1]+=["orange"]b[2]+=["frog"]b=>[["苹果"],["橙子"],["Frog"]]通过推送，我将推送的元素附加到每个子数组(为什么？):a=Array.new(3,[])a[0].push("apple")a[1].push("orange")a[2].push("frog")a=>[[“苹果”、“橙子”、“Frog”]、[“苹果”、“橙子”、“Frog”]、[“苹果”、“
我正在使用Ruby解决一些ProjectEuler问题，特别是这里我要讨论的问题25(Fibonacci数列中包含1000位数字的第一项的索引是多少？)。起初，我使用的是Ruby2.2.3，我将问题编码为:number=3a=1b=2whileb.to_s.length但后来我发现2.4.2版本有一个名为digits的方法，这正是我需要的。我转换为代码:whileb.digits.length当我比较这两种方法时，digits慢得多。时间./025/problem025.rb0.13s用户0.02s系统80%cpu0.190总计./025/problem025.rb2.19s用户0.0
我正在寻找一个用ruby演示计时器的在线示例，并发现了下面的代码。它按预期工作，但这个简单的程序使用30Mo内存(如Windows任务管理器中所示)和太多CPU有意义吗？非常感谢deftime_blockstart_time=Time.nowThread.new{yield}Time.now-start_timeenddefrepeat_every(seconds)whiletruedotime_spent=time_block{yield}#Tohandle-vesleepinteravalsleep(seconds-time_spent)iftime_spent
如果用户是所有者，我有一个条件来检查说删除和文章。delete_articleifuser.owner?另一种方式是user.owner?&&delete_article选择它有什么好处还是它只是一种写作风格 最佳答案 性能不太可能成为该声明的问题。第一个要好得多-它更容易阅读。您future的自己和其他将开始编写代码的人会为此感谢您。 关于ruby-on-rails-如果条件与&&，是否有任何性能提升，我们在StackOverflow上找到一个类似的问题：
有没有办法让Ruby能够做这样的事情？classPlane@moved=0@x=0defx+=(v)#thisiserror@x+=v@moved+=1enddefto_s"moved#{@moved}times,currentxis#{@x}"endendplane=Plane.newplane.x+=5plane.x+=10putsplane.to_s#moved2times,currentxis15 最佳答案 您不能在Ruby中覆盖复合赋值运算符。任务在内部处理。您应该覆盖+，而不是+=。plane.a+=b与plane.a=
出于某种原因，heroku尝试要求dm-sqlite-adapter，即使它应该在这里使用Postgres。请注意，这发生在我打开任何URL时-而不是在gitpush本身期间。我构建了一个默认的Facebook应用程序。gem文件:source:gemcuttergem"foreman"gem"sinatra"gem"mogli"gem"json"gem"httparty"gem"thin"gem"data_mapper"gem"heroku"group:productiondogem"pg"gem"dm-postgres-adapter"endgroup:development,:t
我是Ruby和这个网站的新手。下面两个函数是不同的，一个在函数外修改变量，一个不修改。defm1(x)x我想确保我理解正确-当调用m1时，对str的引用被复制并传递给将其视为x的函数。运算符当调用m2时，对str的引用被复制并传递给将其视为x的函数。运算符+创建一个新字符串，赋值x=x+"4"只是将x重定向到新字符串，而原始str变量保持不变。对吧？谢谢 最佳答案 String#+::str+other_str→new_strConcatenation—ReturnsanewStringcontainingother_strconc