{"id":5562,"date":"2021-09-15T16:55:58","date_gmt":"2021-09-15T08:55:58","guid":{"rendered":"https:\/\/damogame.cn:15443\/wordpress\/?p=5562"},"modified":"2021-09-15T16:55:58","modified_gmt":"2021-09-15T08:55:58","slug":"c17%e4%bd%bf%e7%94%a8stdapply%e5%92%8cfold-expression%e5%af%b9stdtuple%e8%bf%9b%e8%a1%8c%e9%81%8d%e5%8e%86","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/5562","title":{"rendered":"C++17\u4f7f\u7528std::apply\u548cfold expression\u5bf9std::tuple\u8fdb\u884c\u904d\u5386"},"content":{"rendered":"
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\u539f\u6587\u5730\u5740<\/a> <\/p>\n

\u5148\u6765\u770b\u8fd9\u4e2astd::apply<\/code>\u51fd\u6570\uff0c\u8fd9\u4e2a\u51fd\u6570\u5b9a\u4e49\u5728tuple<\/code>\u5934\u6587\u4ef6\u4e2d\uff0c\u51fd\u6570\u7b7e\u540d\u5982\u4e0b\uff1a<\/p>\n

template <<\/span>class F,<\/span> class Tuple><\/span>\r\nconstexpr decltype<\/span>(<\/span>auto<\/span>)<\/span> apply<\/span>(<\/span>F&&<\/span> f,<\/span> Tuple&&<\/span> t)<\/span>;<\/span><\/code><\/pre>\n
<\/code><\/pre>\n
\u8be5\u51fd\u6570\u63a5\u53d7\u4e24\u4e2a\u53c2\u6570\uff0c\u7b2c\u4e00\u4e2a\u662f\u4e00\u4e2a\u51fd\u6570\u5bf9\u8c61\uff0c\u7b2c\u4e8c\u4e2a\u662f\u4e00\u4e2aTuple\u5bf9\u8c61<\/p>\n
\u6765\u770b\u4e00\u4e2a\u6700\u7b80\u5355\u7684\u793a\u4f8b\uff1a<\/p>\n
#include<\/span> <tuple><\/span><\/span>\r\n#include<\/span> <iostream><\/span><\/span>\r\n\r\nint<\/span> main<\/span>(<\/span>)<\/span> {<\/span>\r\n    \/\/ \u4e24\u4e2a\u5143\u7d20\u76f8\u52a0<\/span>\r\n    std:<\/span>:<\/span>cout <<<\/span> std:<\/span>:<\/span>apply<\/span>(<\/span>[<\/span>]<\/span>(<\/span>auto<\/span> x,<\/span> auto<\/span> y)<\/span> {<\/span> return<\/span> x +<\/span> y;<\/span> }<\/span>,<\/span> \r\n                            std:<\/span>:<\/span>make_tuple<\/span>(<\/span>1<\/span>,<\/span> 2.0<\/span>)<\/span>)<\/span> <<<\/span> '\\n'<\/span>;<\/span>\r\n}<\/span><\/code><\/pre>\n
<\/code><\/pre>\n
\u8f93\u51fa\u7ed3\u679c\u662f3<\/p>\n
\u8fd9\u4e2a\u4f8b\u5b50\u4e2d\u7b2c\u4e00\u4e2a\u53c2\u6570\u4f7f\u7528Lambda\u533f\u540d\u51fd\u6570\u5c06tuple<\/code>\u4e2d\u7684\u4e24\u4e2a\u5143\u7d20\u76f8\u52a0\uff0c\u7b2c\u4e8c\u4e2a\u4f7f\u7528std::make_tuple<\/code>\u51fd\u6570\u6784\u9020\u4e00\u4e2a\u53ea\u542b\u6709\u4e24\u4e2a\u5143\u7d20\u7684tuple<\/code><\/p>\n
<\/a><\/a>fold expression<\/h2>\n
\u8fd9\u4e2a\u7279\u6027\u662fC++ 17\u4e2d\u6211\u89c9\u5f97\u5f88\u6709\u7528\u7684\u4e00\u4e2a\u65b0\u7279\u6027\uff0c\u4f7f\u7528\u89c4\u5219\u6709\u4e0b\u9762\u56db\u6761\uff1a<\/p>\n
    \n
  1. Unary right fold ( E E <\/span>E<\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> \u2026) becomes ( E 1 E_1 <\/span>E<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> (\u2026  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> ( E N \u2212 1 E_{N-1} <\/span>E<\/span>N<\/span>\u2212<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E N E_N <\/span>E<\/span>N<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)))<\/li>\n
  2. Unary left fold (\u2026  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E E <\/span>E<\/span><\/span><\/span><\/span><\/span>) becomes ((( E 1 E_1 <\/span>E<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E 2 E_2 <\/span>E<\/span>2<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> \u2026)  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E N E_N <\/span>E<\/span>N<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)<\/li>\n
  3. Binary right fold ( E E <\/span>E<\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> \u2026  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  I I <\/span>I<\/span><\/span><\/span><\/span><\/span>) becomes ( E 1 E_1 <\/span>E<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> (\u2026  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> ( E N \u2212 1 E_{N\u22121} <\/span>E<\/span>N<\/span>\u22121<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> ( E N E_N <\/span>E<\/span>N<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  I I <\/span>I<\/span><\/span><\/span><\/span><\/span>))))<\/li>\n
  4. Binary left fold ( I I <\/span>I<\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> \u2026  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E E <\/span>E<\/span><\/span><\/span><\/span><\/span>) becomes (((( I I <\/span>I<\/span><\/span><\/span><\/span><\/span>  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E 1 E_1 <\/span>E<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E 2 E_2 <\/span>E<\/span>2<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span> \u2026)  o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>  E N E_N <\/span>E<\/span>N<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>)<\/li>\n<\/ol>\n
    \u8fd9\u91cc\u7684 E E <\/span>E<\/span><\/span><\/span><\/span><\/span>\u6307\u7684\u662fExpression\uff08\u7b26\u5408C++\u8bed\u6cd5\u7684\u8868\u8fbe\u5f0f\uff09\uff0c o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>\u6307\u7684\u662foperator\uff08\u64cd\u4f5c\u7b26\uff09\uff0c N N <\/span>N<\/span><\/span><\/span><\/span><\/span>\u662fparameter pack\uff08\u53ef\u53d8\u53c2\u6570\uff09\u7684\u4e2a\u6570\uff0c I I <\/span>I<\/span><\/span><\/span><\/span><\/span>\u662f\u4e00\u4e2a\u5e38\u6570\u3002<\/p>\n
    \u53ef\u80fd\u770b\u8fd9\u4e2a\u89c4\u5219\u6709\u4e9b\u62bd\u8c61\uff0c\u6211\u4eec\u6765\u770b\u4e00\u4e9b\u5177\u4f53\u7684\u4f8b\u5b50\uff1a<\/p>\n
    #include<\/span> <tuple><\/span><\/span>\r\n#include<\/span> <iostream><\/span><\/span>\r\n\r\nint<\/span> main<\/span>(<\/span>)<\/span> {<\/span>\r\n    \/\/ \u591a\u4e2a\u5143\u7d20\u76f8\u52a0\uff0c\u4f7f\u7528parameter pack<\/span>\r\n    std:<\/span>:<\/span>cout <<<\/span> std:<\/span>:<\/span>apply<\/span>(<\/span>[<\/span>]<\/span>(<\/span>auto<\/span>&&<\/span> .<\/span>.<\/span>.<\/span> args)<\/span> {<\/span> return<\/span> (<\/span>args +<\/span> .<\/span>.<\/span>.<\/span>)<\/span>;<\/span> }<\/span>,<\/span>\r\n                            std:<\/span>:<\/span>make_tuple<\/span>(<\/span>1<\/span>,<\/span> 2.f<\/span>,<\/span> 3.0<\/span>)<\/span>)<\/span> <<<\/span> '\\n'<\/span>;<\/span>\r\n    \/\/ \u904d\u5386tuple\u5e76\u8f93\u51fa\uff0c\u6ce8\u610f\u9017\u53f7\u64cd\u4f5c\u7b26\u7684\u4f7f\u7528<\/span>\r\n    std:<\/span>:<\/span>apply<\/span>(<\/span>[<\/span>]<\/span>(<\/span>auto<\/span>&&<\/span>.<\/span>.<\/span>.<\/span> args)<\/span> {<\/span> (<\/span>(<\/span>std:<\/span>:<\/span>cout <<<\/span> args <<<\/span> '\\n'<\/span>)<\/span>,<\/span> .<\/span>.<\/span>.<\/span>)<\/span>;<\/span> }<\/span>,<\/span>\r\n                std:<\/span>:<\/span>make_tuple<\/span>(<\/span>1<\/span>,<\/span> 2.f<\/span>,<\/span> 3.0<\/span>)<\/span>)<\/span>;<\/span>\r\n}<\/span><\/code><\/pre>\n
    <\/code><\/pre>\n
    \u8f93\u51fa\u5982\u4e0b\uff1a<\/p>\n
    6\r\n1\r\n2\r\n3<\/code><\/pre>\n
    <\/code><\/pre>\n
    \u7b2c6\u884c\u4e2d\uff0cstd::apply<\/code>\u51fd\u6570\u7684\u7b2c\u4e00\u4e2a\u53c2\u6570\u662f\u4e00\u4e2aLambda\u533f\u540d\u51fd\u6570\uff0c\u51fd\u6570\u7684\u53c2\u6570\u662f\u4e00\u4e2a\u53ef\u53d8\u53c2\u6570args<\/code>\uff0c\u51fd\u6570\u4f53\u4e2d\u53ea\u6709\u4e00\u6761\u8bed\u53e5args + ...<\/code>\uff0c\u8fd9\u4e2a\u60c5\u51b5\u5c31\u662f\u4e0a\u9762\u7684\u7b2c\u4e00\u79cd\u60c5\u51b5\uff1a\u8fd9\u91cc\u7684 E E <\/span>E<\/span><\/span><\/span><\/span><\/span>\u5c31\u662fargs<\/code>\uff0c o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>\u5c31\u662f+<\/code>\uff0c\u6240\u4ee5\u5c55\u5f00\u6765\u5c31\u662f a r g s 1 + a r g s 2 + a r g s 3 args_1 + args_2 + args_3 <\/span>a<\/span>r<\/span>g<\/span>s<\/span>1<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span>+<\/span><\/span>a<\/span>r<\/span>g<\/span>s<\/span>2<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span>+<\/span><\/span>a<\/span>r<\/span>g<\/span>s<\/span>3<\/span><\/span><\/span><\/span>\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span>\uff08\u56e0\u4e3a\u53c2\u6570\u7684\u4e2a\u6570\u662f3\uff09\u3002<\/p>\n
    \u7b2c9\u884c\u4e2d\uff0cLambda\u533f\u540d\u51fd\u6570\u7684\u51fd\u6570\u4f53\u662f((std::cout << args << '\\n'), ...)<\/code>\u8fd9\u662f\u4e00\u4e2a\u9017\u53f7\u64cd\u4f5c\u7b26\uff0c\u4e5f\u5c5e\u4e8e\u4e0a\u9762\u56db\u79cd\u60c5\u51b5\u4e2d\u7684\u7b2c\u4e00\u79cd\uff1a\u8fd9\u91cc\u7684 E E <\/span>E<\/span><\/span><\/span><\/span><\/span>\u5c31\u662fstd::cout << args << '\\n')<\/code>\uff0c o p op <\/span>o<\/span>p<\/span><\/span><\/span><\/span><\/span>\u5c31\u662f,<\/code>\uff0c\u6240\u4ee5\u8fd9\u4e00\u884c\u5c31\u6253\u5370\u8f93\u51fa\u4e86tuple<\/code>\u7684\u6bcf\u4e00\u4e2a\u5143\u7d20\u3002\u5982\u679c\u5728C++17\u4e4b\u524d\u60f3\u8981\u904d\u5386tuple<\/code>\u5c31\u6bd4\u8f83\u9ebb\u70e6\uff0c\u9700\u8981\u5f88\u591a\u989d\u5916\u7684\u64cd\u4f5c\u3002<\/p>\n
    <\/a><\/a>\u53c2\u8003\u8d44\u6599<\/h2>\n
      \n
    1. std::apply<\/a><\/li>\n
    2. fold expression<\/a><\/li>\n<\/ol>\n<\/div>\n
      \n
      <\/div>\n<\/div>\n<\/div>\n<\/article>\n","protected":false},"excerpt":{"rendered":"
      \u539f\u6587\u5730\u5740  \u5148\u6765\u770b\u8fd9\u4e2astd:<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[],"tags":[119],"class_list":["post-5562","post","type-post","status-publish","format-standard","hentry","tag-03-"],"_links":{"self":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5562","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/comments?post=5562"}],"version-history":[{"count":0,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5562\/revisions"}],"wp:attachment":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/media?parent=5562"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/categories?post=5562"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/tags?post=5562"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}