使用"&:methodname"快捷方式从array.map(&:methodname)中提取字符串作为哈希键，而不是方法名。

Question

大多数Ruby开发者都知道通过像这样做一些事情来节省一些按键次数：

array.map(&:methodname)

不是...而是...

array.map {|x| x.methodname }

有没有一种类似于 &:methodname 快捷方式来调用哈希数组中的“方法”（通过键调用的值）的方法？

在我的情况下，这是使用 JSON API 返回的批处理结果，作为由 JSON 发起的哈希数组。我尝试过这样做：

array.map(&:"keyname")

但是不成功，抛出NoMethodError并表示Hash没有'keyname'方法，这是合理的。我想知道是否有一些神奇的方法来模拟ruby的&:...快捷方式用于哈希表。

这是一个实际JSON响应之一，我认为结果只限于5个。

[{"geometry":{"location":{"lat":33.723008,"lng":-78.930593}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/bowling-71.png","id":"095e108208879fe989f2b36e81e38bafe0c17574","name":"Waccamaw Bowling Center","opening_hours":{"open_now":true},"photos":[{"height":612,"html_attributions":["\u003Ca href=\"https://plus.google.com/106701205257534874835\"\u003EAndy Badi\u003C/a\u003E"],"photo_reference":"CoQBeQAAANZ3d4xBep-4jlCnHp0IcCfSr4k6WVnAMDkPNPhlhSTaZ-NICdLaPVxaRW04qK8ko8x5SDScTeImNKWo2qlyF0JYTQpy-elxdZkx58BYQsjCLdtOaBr_yIoKk3NSuBGk7RS9Lf2IWpW0NaBjeAcPTNdKKHoTt_PZ4212cD67wV0jEhBmRx62d9nUyBmPkrv51nadGhTXEhV-hA5frdzGKal4tEd2pYPtjQ","width":816}],"rating":3.1,"reference":"CoQBeAAAAD5d1gIGf4AG427DlKp-AC74Wt5ZCTd6uPU0-31qTnDRW3mBk4Scq00zjaLpbXnqvs1rlMgEFHPVId9nPGU5oaWr2nYRqRodz5LGdVpZqHx1R_PRciZX7xb068t6c7bqw7Fy_Bs9YIi8pCNdfAdHEZb8Pjxy1mpnL1qN_DBz243eEhCrzUmU34savXzZijjlv8TzGhSX3SofvWtuGYOhhPol9atp3aTSyQ","types":["bowling_alley","establishment"],"vicinity":"101 Philip Gray Drive, Myrtle Beach"},{"geometry":{"location":{"lat":33.817622,"lng":-78.692496}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/bowling-71.png","id":"12fed6fbc66c7d9fc693fe37e6834e32ee6e23b9","name":"North Myrtle Beach Bowling Center","photos":[{"height":460,"html_attributions":["\u003Ca href=\"https://plus.google.com/100443525307746960711\"\u003EHolly Heniford\u003C/a\u003E"],"photo_reference":"CpQBhwAAADY5u5bWSEVGRZr1A7LR0Dpli5EEDRvOt5oWvzQYCOvRk1XO9bMBPdKvQYy_TwSHDcRRcqo6JZoGyLc-nLvlOoG1gX133KkdJ7lKU33RC9hdeN_dzfAUoxIrArZK8Ssu2QQWpXmq10xsJKPIu2bAzpS3n3vKqLdeKZY86GPw7LR0cM-Su3P0MZiY2AkC7uIJIhIQkQVG3s7We7yNPlqRqBkE4xoULTYXh2O6PPuki5_TXG3tN1O3kLg","width":816}],"reference":"CpQBgwAAAB0eZVssHlDn56UET5IqUpZygTzWdLclQ73lU0xzgNG875YyQPhQWGvOI2ciZq_BO6yZYzjMIdGEFVI-jnOhj_Y56Eq0T1MaLAL0dIkCM9qS4QwjAv3-TjwJOMBnN7aARHr3BuGqYLQZb5fkN3veUr2tWLKDZcPT1SHXRLypDutO5msurlQLub5YgmNhOomPdxIQLbIFLMxiqssFIUbO6bEcrRoU0A49j-VRMk4vHsSqxADOq5OPo1o","types":["bowling_alley","establishment"],"vicinity":"1105 Highway 17S, North Myrtle Bch"},{"geometry":{"location":{"lat":33.617718,"lng":-78.976797}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/bowling-71.png","id":"5b2bcc16481ea7519f5e2858d4aa8af1b836f3c8","name":"Surfside Bowling Center","rating":4.4,"reference":"CoQBeQAAACW_aubzCjtG19Nw9Pm9RIXpzpgXD5rFyKziCYy0Uc7X9g1vVz2YWoDUmXwIYA9uUksSArTypwe8lh76TjYYTnNIPiTXc_dpgw94XGaQwC1dO5DuMBPLtWyKgY4Jqa8UlYdHnTOe4FPJnZV7gTsx25Eid2iasa07gruGui6tltYtEhBpBraa9i7GzEE3FUYWxUU0GhSsfU66SAn8tpT3Oa_PRkTUYLXlCQ","types":["bowling_alley","establishment"],"vicinity":"510 U.S. 17 Business, Surfside Beach"},{"geometry":{"location":{"lat":33.580683,"lng":-79.024837}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/bowling-71.png","id":"259104d58ff8e1aebe70db6149c74c736500a069","name":"Frank Theatres","opening_hours":{"open_now":true},"photos":[{"height":400,"html_attributions":[],"photo_reference":"CnRnAAAAq26m02SGow16WCPVIvqioB646tx-kq39g-KPZ6rydR4gUFS2eFF_M3f0-ntrLiq-Iv3jjiQfUdVt_qMxYSAxxOxhfW9JucBG9-Z4ddJH-teNg6p62rHu5Ebbxs-CI40xoK78w3rdLbYA6GsWaOL5gRIQ5UBFXus-gXSy1UrWQ_aiixoUFE0H2eqxYpFyzbGkQtbq4nUHgUk","width":300}],"reference":"CnRvAAAAMDm7HoTk9pG-nKJGvzl9QIw6Qhso44Nh5Q0-xOwM5rykjQ12DJiF_2vZRMaUk9bOtNJwW9ntoBpTgj6bHtWiVCP3OlMu-gd0dgMygMvrIxGTkaR3cTKab0KuHHnoCFxdVB7esI-rK0v585lWS6xTZxIQ0gFfzO3vhZGkIjF6ThDgNBoUAYAMJyjC7f__SBcqOLKbDl3pFSQ","types":["bowling_alley","restaurant","food","movie_theater","establishment"],"vicinity":"10125 Frontage Road #12f, Murrells Inlet"},{"geometry":{"location":{"lat":33.959856,"lng":-78.400399}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/bowling-71.png","id":"39a632e654125e6aa73a526579cae55cc14ee4a2","name":"Brunswick County Bowling Center","reference":"CoQBgAAAAETfTwuwFT34ynta7FJFME2kBVM0XurlJJKj3IQMaOXlWqTGU2P2L4l3gX9XP3XkGSgbxsQiOxIpGiTkrKRVV_-EzvGMNeE8IpsmSUMY7SBY-w7SlC6DGtlX1Py-YES6ZSTrM36my9f6Y2s7bAqamlvXbdtGfTgJpycuI0cx28fvEhB7Y-gtYgRCIInlgHxli4ygGhQlgaJt7d4PylH0KJBnzjRJeIKbNA","types":["bowling_alley","establishment"],"vicinity":"630 Village Rd SW, South Brunswick"},{"geometry":{"location":{"lat":33.974945,"lng":-78.396355}},"icon":"http://maps.gstatic.com/mapfiles/place_api/icons/generic_business-71.png","id":"abaf128a51021a535a17b1af4a523a5fc3af7d10","name":"Planet Fun","photos":[{"height":485,"html_attributions":[],"photo_reference":"CnRtAAAACFYcotbimoFO1Jrqiy7PgLZ3Uuq4t1BLKvrewRdsV0aUZ4ay1jwtCaDQ-q2sh7EweO5At2YA3Mg-tukES9UXItwOn2uLD2sXenKg2UhkBSwa-bvd4RGAH-dg0uACDU_0_kCi7xHkv5WrgSiKmBVN8hIQYBr23I1W9dOQ5F6Rdn1wfRoUVBdp3FEoKA_0e29nzlnUem15BJs","width":1024}],"rating":2.8,"reference":"CnRrAAAARZu90zQ_rp_pRX80BxqorM2GecSJ9kUkRnWNWEDx5K5JXwe9qgPdkzMsq8yOxITR1iPmS6knSWKNO-eWhYxBtJSti7O0ar1kkK2lBUhS5Kn6AxuT8bxlyuKLSuiGN3Zi-YFXI6d4nxhL7uO3K8LAnxIQNJ5TMpFhegaM3saANGrubBoUD7D9lw61ng3SmpK4g1dzf1cIVJ4","types":["amusement_park","establishment"],"vicinity":"349 Whiteville Road Northwest, Shallotte"}]

- boulder_ruby

---

请给我们提供一个示例..谢谢..只有在了解示例后，我们才会考虑是否有任何技巧..先写出简单的代码，然后告诉我们是否有更聪明的方法可用？ - Arup Rakshit

可能是Ruby和符号快捷方式的重复。 - austinbv

这也被称为“椒盐脆饼”语法（Pretzel Colon Syntax）。 - anothermh

Answer 1

你可以使用lambda实现这个功能：

extract_keyname = ->(h) { h[:keyname] }
ary_of_hashes.map(&extract_keyname)

如果块的逻辑比从哈希中提取一个值更加复杂，那么这种方式往往更加有用。此外，给你的逻辑片段附上名称可以帮助澄清一系列 Enumerable 方法调用试图做什么。

如果您需要多次执行此操作，还可以使用返回 lambda 的 lambda：

extract = ->(k) { ->(h) { h[k] } }
ary_of_hashes.map(&extract[:keyname])
ary_of_hashes.map(&extract[:other_key])

或使用lambda构建方法：

def extract(k)
  ->(h) { h[k] }
end

ary_of_hashes.map(&extract(:keyname))
ary_of_hashes.map(&extract(:other_key))

- mu is too short

Answer 2

如果你正在使用Ruby on Rails，你可以使用Enumerable#pluck方法，该方法由ActiveSupport实现。这将使您能够执行以下操作：

array_of_hashes = [{a: 1, b: 2}, {a: 3,b: 4}, {a: 5, b: 6}]
=> [{:a=>1, :b=>2}, {:a=>3, :b=>4}, {:a=>5, :b=>6}]

array_of_hashes.pluck(:b)
=> [2, 4, 6]

查看文档请点击此处：https://www.rubydoc.info/gems/activesupport/5.0.0/Enumerable:pluck

- Hula_Zell

---

太棒了！！这对我来说很好用。 - Luiz Carvalho

Answer 3

&在Ruby中的一行语句之前是调用to_proc的快捷方式。

对于符号to_proc会在“上下文”中查找该方法并将其用作参考。

还有：

• Ruby &冒号快捷方式
• Ruby中map(&:name)的含义是什么？
• &：运算符在Ruby中的功能是什么？

- austinbv