{"id":7259,"date":"2012-12-25T22:16:50","date_gmt":"2012-12-25T14:16:50","guid":{"rendered":"http:\/\/ihower.tw\/blog\/?p=7259"},"modified":"2013-01-23T21:12:26","modified_gmt":"2013-01-23T13:12:26","slug":"defensive-programming-%e9%98%b2%e7%a6%a6%e6%80%a7%e7%a8%8b%e5%bc%8f%e8%a8%ad%e8%a8%88","status":"publish","type":"post","link":"https:\/\/ihower.tw\/blog\/7259-defensive-programming-%e9%98%b2%e7%a6%a6%e6%80%a7%e7%a8%8b%e5%bc%8f%e8%a8%ad%e8%a8%88","title":{"rendered":"Defensive Programming \u9632\u79a6\u6027\u7a0b\u5f0f\u8a2d\u8a08"},"content":{"rendered":"<p>TL;DR \u907f\u514d Defensive Programming\uff0c\u611b\u7528 Fail Fast \u7b56\u7565\u3002<\/p>\n<p>\u4ec0\u9ebc\u662f\u9632\u79a6\u6027\u7a0b\u5f0f\u8a2d\u8a08\uff0c\u5728 <a href=\"http:\/\/www.erlang.se\/doc\/programming_rules.shtml#HDR11\">Erlang&#8217;s Programming Rules and Conventions: Do not program &#8220;defensively&#8221;<\/a> \u88e1\u9019\u6a23\u8aaa\u660e\uff1a<\/p>\n<blockquote><p>\u9632\u79a6\u6027\u7a0b\u5f0f\u767c\u751f\u5728\u7a0b\u5f0f\u8a2d\u8a08\u5e2b\u4e0d\u76f8\u4fe1\u7cfb\u7d71\u7684\u8f38\u5165(input)\u8cc7\u6599\u6642\u3002\u4e00\u822c\u4f86\u8aaa\u6211\u5011\u4e0d\u9700\u8981\u6e2c\u8a66\u8f38\u5165\u7684\u8cc7\u6599\u4f86\u78ba\u4fdd\u529f\u80fd\u6b63\u5e38\u3002\u7cfb\u7d71\u4e2d\u5927\u90e8\u5206\u7a0b\u5f0f\u78bc\u61c9\u8a72\u53ef\u4ee5\u5047\u8a2d\u8f38\u5165\u7684\u8cc7\u6599\u662f\u6b63\u78ba\u7684\uff0c\u53ea\u6709\u4e00\u5c0f\u90e8\u5206\u7684\u7a0b\u5f0f\u9700\u8981\u771f\u7684\u6aa2\u67e5\u8cc7\u6599\uff0c\u9019\u901a\u5e38\u767c\u751f\u5728\u8cc7\u6599\u7b2c\u4e00\u6b21\u8f38\u5165\u7684\u6642\u5019\u3002\u53ea\u8981\u8cc7\u6599\u5728\u8f38\u5165\u9032\u7cfb\u7d71\u6642\u88ab\u6aa2\u67e5\u904e\uff0c\u90a3\u9ebc\u5c31\u61c9\u8a72\u53ef\u4ee5\u5047\u8a2d\u5b83\u662f\u6b63\u78ba\u7684\u3002<\/p><\/blockquote>\n<p>\u4e5f\u5c31\u662f\u8aaa\uff0c\u7576\u4f60\u4e0d\u76f8\u4fe1\u8f38\u5165\u6642\uff0c\u4f60\u5c31\u5f97\u53bb\u6aa2\u67e5\u5b83\u3002\u6709\u7d93\u9a57\u7684\u7a0b\u5f0f\u8a2d\u8a08\u5e2b\u61c9\u8a72\u90fd\u975e\u5e38\u719f\u6089\u9019\u7a2e\u4f5c\u6cd5\uff0c\u4ed6\u7684\u7f3a\u9ede\u5728\u65bc\u9019\u5e38\u662f\u591a\u9918\u7684\u8cc7\u6e90\u6d6a\u8cbb\uff0c\u4e0d\u4f46\u6d6a\u8cbb\u6548\u80fd\uff0c\u4e5f\u589e\u52a0\u7a0b\u5f0f\u78bc\u7dad\u8b77\u7684\u6210\u672c\u3002\u597d\u6bd4\u8aaa\u4e00\u500b\u65b9\u6cd5\u5df2\u7d93\u6aa2\u67e5\u904e\u53c3\u6578\u4e86\uff0c\u8a72\u65b9\u6cd5\u53c8\u7e7c\u7e8c\u628a\u53c3\u6578\u50b3\u905e\u7d66\u5225\u7684\u65b9\u6cd5\u6642\uff0c\u53ef\u80fd\u53c8\u8981\u518d\u6aa2\u67e5\u4e00\u6b21\u3002\u5982\u679c\u6240\u6709\u65b9\u6cd5\u90fd\u8981\u91dd\u5c0d\u53c3\u6578\u91cd\u8907\u505a\u56b4\u683c\u7684\u6aa2\u67e5\uff0c\u8c48\u4e0d\u662f\u975e\u5e38\u56c9\u55e6\u3002\u6240\u4ee5 Erlang&#8217;s Programming Rules \u5efa\u8b70\u4f60\u5728\u7cfb\u7d71\u88e1\u4e0d\u8981\u6aa2\u67e5\uff0ccrash \u8207\u5426\u7684\u8cac\u4efb\u5728\u65bc\u547c\u53eb\u65b9\uff0c\u5728\u65bc\u8cc7\u6599\u4e00\u958b\u59cb\u8f38\u5165\u9032\u7cfb\u7d71\u7684\u6642\u5019\uff0c\u800c\u4e0d\u662f\u9019\u500b\u65b9\u6cd5\u3002<\/p>\n<p>\u4f46\u662f\uff0c\u7e3d\u662f\u6709\u9700\u8981\u6aa2\u67e5\u7684\u6642\u5019\uff0c\u7279\u5225\u662f\u8cc7\u6599\u7b2c\u4e00\u6b21\u8f38\u5165\u9032\u7cfb\u7d71\u7684\u908a\u754c\u60c5\u6cc1\uff0c\u4ee5\u61c9\u7528\u7a0b\u5f0f\u4f86\u8aaa\uff0c\u5c31\u662f\u6307\u4f7f\u7528\u8005\u7684\u8f38\u5165; \u4ee5 Library \u4f86\u8aaa\uff0c\u5c31\u662f\u6307 Public API\u3002\u9019\u6642\u5019\u6709\u5169\u7a2e\u7b56\u7565\u4f86\u5c0d\u4ed8\u4e0d\u4e56\u7684\u53c3\u6578\uff1a 1. \u4fee\u6b63\u6216\u7565\u904e\u8cc7\u6599\u7684\u932f\u8aa4(defensive, compensate) 2.\u4e1f\u51fa\u932f\u8aa4(offensive, fail fast)<\/p>\n<p>\u8b93\u6211\u5011\u4f86\u770b\u770b\u4f8b\u5b50\u5427\u3002\u4ee5 Check Null \u578b\u7684\u554f\u984c\u4f86\u8aaa\uff0c\u6709\u4e09\u7a2e\u5beb\u6cd5\uff1a<\/p>\n<pre><code># defensive programming\r\n# \u5982\u679c\u53c3\u6578\u4e0d\u7b26\u5408\u689d\u4ef6\uff0c\u5c31\u7565\u904e\u6216\u4fee\u6b63\u5b83\r\ndef resize_image(image)\r\n    if image &amp;&amp; image.is_a?(File) # \u6aa2\u67e5 image \u4e0d\u662f nil\uff0c\u800c\u4e14\u662f File\r\n        # execute code\r\n    else\r\n        # ingore, nothing happened.\r\n    end\r\nend\r\n\r\n# non-defensive programming\r\n# \u4e0d\u6aa2\u67e5\uff0c\u932f\u4e86\u5c31\u8b93\u4ed6 crash \u5427\r\ndef resize_image(image)\r\n    # execute code\r\nend\r\n\r\n# offensive programming (fail fast)\r\n# \u6aa2\u67e5\uff0c\u6709\u932f\u5c31\u99ac\u4e0a\u5931\u6557\u8b93\u4f60\u77e5\u9053\r\ndef resize_image(image)     \r\n  raise \"The image is invalid\" unless ( image &amp;&amp; image.is_a?(File) )                \r\n  # execute code        \r\nend\r\n<\/code><\/pre>\n<p>Daniel Roop \u5728 <a href=\"http:\/\/danielroop.com\/blog\/2009\/10\/15\/why-defensive-programming-is-rubbish\/\">Why Defensive Programming is Rubbish<\/a> \u8a8d\u70ba defensive \u7b56\u7565\u662f\u4e00\u7a2e <em>Hide the Problem Programming<\/em>\uff0c\u6211\u89ba\u5f97\u8b1b\u7684\u5f88\u597d\u3002\u70ba\u4ec0\u9ebc\u547c\u53eb\u65b9\u6703\u50b3\u4e0d\u5c0d\u7684\u503c\u9032\u4f86\u5462? \u9019\u662f\u61c9\u8a72\u8981\u53bb trace \u7684\u554f\u984c\uff0c\u800c\u4e0d\u662f\u628a\u554f\u984c\u96b1\u85cf\u8d77\u4f86\u3002\u9577\u4e45\u4ee5\u5f80\u4e0b\u4f86\uff0c\u6574\u500b\u7cfb\u7d71\u7684\u4e0d\u78ba\u5b9a\u6027\u5c31\u6703\u8d8a\u4f86\u8d8a\u591a\uff0c\u4e5f\u5c31\u8d8a\u4f86\u8d8a\u96e3\u7dad\u8b77\u3002<\/p>\n<p>\u6bd4\u8f03\u5efa\u8b70\u7684\u4f5c\u6cd5\u662f\uff0c\u5982\u679c\u662f\u7cfb\u7d71\u5167\u53ef\u4ee5\u76f8\u4fe1\u547c\u53eb\u65b9\uff0c\u90a3\u5c31\u4e0d\u8981\u6aa2\u67e5\u4e86\u3002\u5982\u679c\u662f\u908a\u754c\u60c5\u6cc1\u9700\u8981\u6aa2\u67e5\uff0c\u5c31\u505a offensive programming\uff0c\u4e5f\u5c31\u662f &#8220;Fail Fast&#8221;\uff0c\u628a\u689d\u4ef6\u9650\u5236\u7576\u505a\u4e00\u7a2e\u5951\u7d04\uff0c\u5982\u679c\u547c\u53eb\u65b9(caller)\u4e0d\u7167\u898f\u77e9\u4f86\uff0c\u6574\u500b\u65b9\u6cd5\u5c31\u6703 fail \u6389\uff0c\u9019\u6a23\u7684\u597d\u8655\u662f\u53ef\u4ee5\u63d0\u65e9\u767c\u73fe\u554f\u984c\uff0c\u4e26\u4e14\u5728\u554f\u984c\u767c\u751f\u7684\u7b2c\u4e00\u6642\u9593\u5c31\u53ef\u4ee5\u4fee\u597d\uff0c\u8b93\u6574\u500b\u7cfb\u7d71\u671d\u5411\u53ef\u4ee5\u4e92\u76f8\u4fe1\u4efb\u7684\u65b9\u5411\u6210\u9577\u3002<\/p>\n<p>\u518d\u8209\u4e00\u500b\u66f4\u60e1\u540d\u662d\u5f70\u7684 defensive programming \u7684\u4f8b\u5b50\uff1a<\/p>\n<pre><code># defensive programming\r\ndef run\r\n    # execute code      \r\n    rescue  # \u6551\u56de\u6240\u6709\u4f8b\u5916\r\nend\r\n<\/code><\/pre>\n<p>\u6b64\u4f8b\u4e2d\uff0c\u7121\u8ad6\u767c\u751f\u4ec0\u9ebc\u932f\u8aa4\uff0c\u9019\u500b\u65b9\u6cd5\u90fd\u6703\u56de\u50b3 nil\uff0c\u975e\u5e38\u5b89\u5168\u4e0d\u6703 crash\u3002\u4f46\u662f\u5373\u4f7f execute code \u7684\u5730\u65b9\u6253\u932f\u5b57\u4e5f\u4e0d\u6703\u600e\u6a23\uff0c\u5fb9\u5e95\u628a\u554f\u984c\u96b1\u85cf\u8d77\u4f86\u4e86\u3002<\/p>\n<h2>\u53ef\u662f&#8230;.<\/h2>\n<p>\u53ef\u662f\u6211\u5011\u8a2d\u8a08API\u7684\u6642\u5019\uff0c\u7279\u5225\u662f\u50cf Ruby \u9019\u7a2e\u52d5\u614b\u8a9e\u8a00\uff0c\u5e38\u5e38\u5141\u8a31\u53c3\u6578\u5f88\u6709\u5f48\u6027\u8036? \u4f8b\u5982<\/p>\n<pre><code> # \u53c3\u6578 i \u9664\u4e86\u53ef\u4ee5\u662f\u6578\u5b57\u4e4b\u5916\uff0c\u4e5f\u53ef\u4ee5\u662f\u5b57\u4e32\uff0c\u4f8b\u5982 \"123\"\r\ndef process_integer(i)\r\n    var = i.to_i # \u8f49\u6578\u5b57\r\n    # process var\r\nend\r\n\r\n# \u53c3\u6578 s \u9664\u4e86\u53ef\u4ee5\u662f\u5b57\u4e32\u4e4b\u5916\uff0c\u4e5f\u53ef\u4ee5\u662f Symbol \u6216\u6578\u5b57\u7b49\r\ndef process_string(s)\r\n    var = s.to_s # \u8f49\u5b57\u4e32\r\n    # process var\r\nend\r\n\r\n# \u53c3\u6578 a \u9664\u4e86\u53ef\u4ee5\u662f\u9663\u5217\u4e4b\u5916\uff0c\u4e5f\u53ef\u4ee5\u53ea\u50b3\u4e00\u500b\u5143\u7d20\u6216nil\r\ndef process_array(a)\r\n    arr = Array(a) # \u8b93 arr \u4e00\u5b9a\u662f\u9663\u5217\r\n    arr.each do |x|\r\n        # process x\r\n    end\r\nend\r\n<\/code><\/pre>\n<p>\u597d\u5427\uff0c\u9019\u7a2e\u7b97\u662f&#8221;\u6709\u610f (intentional)&#8221;\u7684 API \u8a2d\u8a08\uff0c\u6211\u5011\u64f4\u5927\u4e86\u53c3\u6578\u7684\u5f48\u6027\uff0c\u800c\u4e14\u547c\u53eb\u65b9(caller)\u660e\u78ba\u77e5\u9053\u53ef\u4ee5\u9019\u6a23\u547c\u53eb(\u6700\u597d\u642d\u914dAPI\u6587\u4ef6)\u3002\u5728 <a href=\"http:\/\/devblog.avdi.org\/2012\/06\/05\/confident-ruby-beta\/\">Confident Ruby<\/a> \u9019\u672c\u66f8\u88e1\uff0c\u63d0\u5230\u4e86\u5f88\u591a Ruby \u9069\u7528\u7684\u6280\u5de7\u3002<\/p>\n<h2>Contract by Design<\/h2>\n<p>\u53e6\u4e00\u7a2e\u89e3\u6c7a\u6aa2\u67e5\u53c3\u6578\u524d\u7f6e\u6027\u689d\u4ef6\u7684\u6839\u672c\u65b9\u6cd5\uff0c\u53eb\u505a&#8221;\u5951\u7d04\u5f0f\u8a2d\u8a08 Contract by Design&#8221;\uff0c\u4e5f\u5c31\u662f\u5728\u8a9e\u8a00\u5c64\u9762\u53bb\u5ba3\u544a\u524d\u7f6e\u689d\u4ef6\u3002\u4e0d\u904e\uff0c\u5927\u90e8\u5206\u7684\u7a0b\u5f0f\u8a9e\u8a00\u90fd\u6c92\u6709\u5167\u5efa\uff0cRuby \u662f\u6709\u4e00\u4e9b\u7b2c\u4e09\u65b9\u5957\u4ef6(\u5229\u7528Ruby\u7684meta-programming\u7279\u6027\u4f86\u505a)\uff0c\u4e0d\u904e\u7528\u7684\u4eba\u5c31\u4e0d\u591a\u4e86\u3002<\/p>\n<ul>\n<li><a href=\"http:\/\/en.wikipedia.org\/wiki\/Design_by_contract\">Design by contract<\/a><\/li>\n<li><a href=\"https:\/\/github.com\/egonSchiele\/contracts.ruby\">github.com\/egonSchiele\/contracts.ruby<\/a><\/li>\n<li><a href=\"https:\/\/github.com\/bguthrie\/handshake\">github.com\/bguthrie\/handshake<\/a><\/li>\n<\/ul>\n<h2>\u7d50\u8ad6<\/h2>\n<ol>\n<li>\u5728\u7cfb\u7d71\u908a\u754c\u5167\uff0c\u76e1\u91cf\u76f8\u4fe1\u8f38\u5165\uff0c\u4e0d\u505a\u6aa2\u67e5<\/li>\n<li>\u5982\u679c\u9700\u8981\u6aa2\u67e5\uff0c\u63a1\u7528\u6709\u932f\u8aa4\u5c31\u4e2d\u65b7\u6389\u7684\u65b9\u5f0f(Fail-fast)\uff0c\u907f\u514d defensive programming \u628a\u554f\u984c\u85cf\u8d77\u4f86<\/li>\n<\/ol>\n<h2>\u5f8c\u8a71<\/h2>\n<p>\u53e6\u4e00\u500b\u6703\u8b93\u6574\u500b\u7cfb\u7d71\u5145\u6eff\u9632\u79a6\u6027\u98a8\u683c\u7684\u60c5\u6cc1\uff0c\u53ef\u80fd\u767c\u751f\u5728\u5718\u968a\u611f\u60c5\u4e0d\u597d\u7684\u74b0\u5883\u3002\u70ba\u4ec0\u9ebc\u5462? \u56e0\u70ba\u6e9d\u901a\u4e0d\u826f\uff0c\u52a0\u4e0a\u6c92\u6709\u9069\u7576\u7684\u898f\u7bc4\uff0c\u6240\u4ee5\u5bebcode\u7684\u6642\u5019\u53ea\u597d\u8655\u8655\u9632\u8457\u5225\u4eba\uff0c\u70ba\u4e86\u6015 crash \u8981\u9ebb\u7169\u5225\u4eba(caller)\uff0c\u53ea\u597d\u984d\u5916\u8cbb\u5de5\u52a0\u4e00\u5927\u5806\u591a\u9918\u7684\u689d\u4ef6\u6aa2\u67e5\u548c\u8655\u7406\uff0c\u628a\u554f\u984c\u90fd\u57cb\u8d77\u4f86\u597d\u8b93\u65b9\u6cd5\u4e0d\u6703crash&#8230;<\/p>\n<h2>\u53c3\u8003\u8cc7\u6599<\/h2>\n<ul>\n<li><a href=\"http:\/\/danielroop.com\/blog\/2009\/10\/15\/why-defensive-programming-is-rubbish\/\">Why Defensive Programming is Rubbish<\/a><\/li>\n<li><a href=\"http:\/\/en.wikipedia.org\/wiki\/Defensive_programming\">Defensive programming<\/a> (wikipedia)<\/li>\n<li><a href=\"http:\/\/en.wikibooks.org\/wiki\/Visual_Basic\/Effective_Programming#Avoid_Defensive_Programming.2C_Fail_Fast_Instead\">Avoid Defensive Programming, Fail Fast Instead<\/a><\/li>\n<li><a href=\"http:\/\/c2.com\/cgi\/wiki?OffensiveProgramming\">Offensive Programming<\/a><\/li>\n<li><a href=\"http:\/\/raptorious.com\/2012\/08\/failfast-programming-for-the-lazy-programmer\/\">Failfast programming for the lazy programmer<\/a><\/li>\n<li><a href=\"http:\/\/avdi.org\/talks\/confident-code-rubymidwest-2011\/confident-code.html\">Confident Code<\/a><\/li>\n<li><a href=\"http:\/\/pbrisbin.com\/posts\/be_assertive\">Be Assertive with Sane Exception Handling<\/a><\/li>\n<li>\u7a0b\u5f0f\u8a2d\u8a08\u7bc4\u5f0f\u8207OOP\u7684\u601d\u8003\u8853 p.186<\/li>\n<li>Complete Complete 2nd. \u7b2c\u516b\u7ae0<\/li>\n<li>The Pragmatic Programmer \u7b2c\u56db\u7ae0<\/li>\n<\/ul>\n<p>\u8a3b: \u6709\u4e9b\u4eba\u8a8d\u70ba &#8220;fail fast&#8221; \u4e5f\u7b97\u662f defensive programming \u7684\u4e00\u62db\u3002\u6211\u9019\u88e1\u63a1\u7528\u5c0d\u6bd4\u7684 offensive programming \u8aaa\u6cd5\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>TL;DR \u907f\u514d Defensive Programming\uff0c\u611b\u7528 Fail Fast \u7b56\u7565\u3002 \u4ec0\u9ebc\u662f\u9632\u79a6\u6027\u7a0b &hellip; <\/p>\n<p class=\"link-more\"><a href=\"https:\/\/ihower.tw\/blog\/7259-defensive-programming-%e9%98%b2%e7%a6%a6%e6%80%a7%e7%a8%8b%e5%bc%8f%e8%a8%ad%e8%a8%88\" class=\"more-link\">\u95b1\u8b80\u5168\u6587<span class=\"screen-reader-text\">\u3008Defensive Programming \u9632\u79a6\u6027\u7a0b\u5f0f\u8a2d\u8a08\u3009<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[5,31],"tags":[],"class_list":["post-7259","post","type-post","status-publish","format-standard","hentry","category-programming","category-ruby","entry"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p1q6tG-1T5","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/posts\/7259","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/comments?post=7259"}],"version-history":[{"count":26,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/posts\/7259\/revisions"}],"predecessor-version":[{"id":7595,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/posts\/7259\/revisions\/7595"}],"wp:attachment":[{"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/media?parent=7259"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/categories?post=7259"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ihower.tw\/blog\/wp-json\/wp\/v2\/tags?post=7259"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}