String(42) 在 Ruby 中起什么作用？
为什么我不能这样做？
>> s = String
>> s(42)
s(42)
NoMethodError: undefined method `s' for main:Object
from (irb):86
from /home/sam/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'
下一个。
>> String.new 42
String.new 42
TypeError: can't convert Fixnum into String
from (irb):90:in `initialize'
from (irb):90:in `new'
from (irb):90
from /home/sam/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'
如果 String.new 不能，String() 如何将 Fixnum 转换为 String？我假设 String() 调用 to_s。但是，除了要复制的字符串之外，String.new 还在寻找什么呢？ new 是 dup 的别名吗？
Why cant I do this?
>> s = String
>> s(42)
s(42)
NoMethodError: undefined method `s' for main:Object
from (irb):86
from /home/sam/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'
Next.
>> String.new 42
String.new 42
TypeError: can't convert Fixnum into String
from (irb):90:in `initialize'
from (irb):90:in `new'
from (irb):90
from /home/sam/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in `<main>'
How does String() convert a Fixnum to a String if String.new cannot? I assume String() calls to_s. But then what is String.new looking for besides a string to copy? Is new an alias for dup?
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s(42)在您的示例中不起作用的原因是，有一个名为String的常量（指向该类）以及一个名为 < code>String （使用to_s将参数转换为字符串）。当您执行s = String时，s现在将指向与String相同的类。但是，当您调用s(42)时，Ruby 将查找名为s的方法，该方法不存在，并且您会收到错误。这里的关键是，在 ruby 中，可以存在同名的变量或常量和方法，但它们之间没有任何关系。
String(42)和String.new(42)之间行为不同的原因是String调用to_s和String.new调用to_str。The reason that
s(42)does not work in your example, is that there is a constant namedString(which points to the class) as well as a method namedString(which converts the argument to a string usingto_s). When you dos = String,swill now point to the same class asString. However when you calls(42), ruby will look for a method nameds, which does not exist and you get an error.The key here is that in ruby there can be a variable or constant and a method with the same name without them having anything to do with each other.
The reason for the differing behaviour between
String(42)andString.new(42)is thatStringcallsto_sandString.newcallsto_str.如果您只想要一个包含值“42”的字符串，则只需
s = "42"即可。如果您已有一个要存储为字符串的 Fixnum，
s = some_fixnum.to_s即可实现。If you just want a string with the value "42" in it, then
s = "42"is all you need to do.If you already have a Fixnum that you want to store as a string,
s = some_fixnum.to_swill do it.