为什么符号不是冻结字符串?

尽管它非常反对 DuckTyping，但人们还是倾向于使用 case在类上，并且 Symbol 所以你的问题的答案仍然是:Symbol 就像一个 String，但它不是.问题不在于 Symbol 不应该是 String，而是历史上不是.I understand the theoretical difference between Strings and Symbols. I understand that Symbols are meant to represent a concept or a name or an identifier or a label or a key, and Strings are a bag of characters. I understand that Strings are mutable and transient, where Symbols are immutable and permanent. I even like how Symbols look different from Strings in my text editor.What bothers me is that practically speaking, Symbols are so similar to Strings that the fact that they're not implemented as Strings causes a lot of headaches. They don't even support duck-typing or implicit coercion, unlike the other famous "the same but different" couple, Float and Fixnum.The biggest problem, of course, is that hashes coming into Ruby from other places, like JSON and HTTP CGI, use string keys, not symbol keys, so Ruby programs have to bend over backwards to either convert these up front or at lookup time. The mere existence of HashWithIndifferentAccess, and its rampant use in Rails and other frameworks, demonstrates that there's a problem here, an itch that needs to be scratched.Can anyone tell me a practical reason why Symbols should not be frozen Strings? Other than "because that's how it's always been done" (historical) or "because symbols are not strings" (begging the question).Consider the following astonishing behavior::apple == "apple" #=> false, should be true:apple.hash == "apple".hash #=> false, should be true{apples: 10}["apples"] #=> nil, should be 10{"apples" => 10}[:apples] #=> nil, should be 10:apple.object_id == "apple".object_id #=> false, but that's actually fineAll it would take to make the next generation of Rubyists less confused is this:class Symbol < String def initialize *args super self.freeze end(and a lot of other library-level hacking, but still, not too complicated)See also:http://onestepback.org/index.cgi/Tech/Ruby/SymbolsAreNotImmutableStrings.redhttp://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbolWhy does my code break when using a hash symbol, instead of a hash string?Why use symbols as hash keys in Ruby?What are symbols and how do we use them?Ruby Symbols vs Strings in HashesCan't get the hang of symbols in Rubyhttp://blog.arkency.com/could-we-drop-symbols-from-ruby/Do Ruby symbols exist because strings are mutable and not interned?Update: I think Matz makes the case for class Symbol < String very well here: http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-core/9192 (thanks to Azolo for digging this up, and also Matz' eventual retraction). 解决方案 This answer drastically different from my original answer, but I ran into a couple interesting threads on the Ruby mailing list. (Both good reads)So, at one point in 2006, matz implemented the Symbol class as Symbol < String. Then the Symbol class was stripped down to remove any mutability. So a Symbol was in fact a immutable String.However, it was reverted. The reason given was Even though it is highly against DuckTyping, people tend to use case on classes, and Symbol < String often cause serious problems.So the answer to your question is still: a Symbol is like a String, but it isn't.The problem isn't that a Symbol shouldn't be String, but instead that it historically wasn't. 这篇关于为什么符号不是冻结字符串?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！