新手应该注意哪些 Ruby 陷阱? [英] What are the Ruby Gotchas a newbie should be warned about?

问题描述

我最近学习了 Ruby 编程语言，总而言之，它是一门很好的语言.但是我很惊讶地发现它并不像我想象的那么简单.更准确地说，我似乎不太尊重最小惊喜规则"(当然这是非常主观的).例如:

I have recently learned the Ruby programming language, and all in all it is a good language. But I was quite surprised to see that it was not as simple as I had expected. More precisely, the "rule of least-surprise" did not seem very respected to me (of course this is quite subjective). For example:

x = true and false
puts x  # displays true!

和著名的:

puts "zero is true!" if 0  # zero is true!

您会警告 Ruby 新手的其他陷阱"是什么?

What are the other "Gotchas" you would warn a Ruby newbie about?

推荐答案

维基百科 Ruby 问题

来自文章:

• 以大写字母开头的名称被视为常量，因此局部变量应以小写字母开头.
• 字符 $ 和 @ 不像 Perl 那样指示变量数据类型，而是用作作用域解析运算符.
• 要表示浮点数，必须后跟零位 (99.0) 或显式转换 (99.to_f).附加一个点 (99.) 是不够的，因为数字容易受到方法语法的影响.
• 对非布尔数据的布尔求值是严格的:0、"" 和 [] 都被求值为 true.在 C 中，表达式 0 ?1 : 0 计算结果为 0(即假).然而，在 Ruby 中，它产生 1，因为所有数字的计算结果都是 true；只有 nil 和 false 评估为 false.这个规则的一个推论是，Ruby 方法按照约定——例如，正则表达式搜索——在成功时返回数字、字符串、列表或其他非假值，但在失败时返回 nil(例如，不匹配).这个约定也用于 Smalltalk，其中只有特殊对象 true 和 false 可以用于布尔表达式.
• 1.9 之前的版本缺少字符数据类型(与 C 相比，C 为字符提供类型 char).这在对字符串进行切片时可能会引起意外:"abc"[0] 产生 97(一个整数，表示字符串中第一个字符的 ASCII 码)；获取 "a" 使用 "abc"[0,1](长度为 1 的子串)或 "abc"[0].chr>.

• 符号statement until expression，不同于其他语言的等价语句(例如do { statement } while (not(expression)); in C/C++/...)，如果表达式已经是 true，则实际上永远不会运行该语句.这是因为 statement until expression 实际上是语法糖

• Names which begin with a capital letter are treated as constants, so local variables should begin with a lowercase letter.
• The characters $ and @ do not indicate variable data type as in Perl, but rather function as scope resolution operators.
• To denote floating point numbers, one must follow with a zero digit (99.0) or an explicit conversion (99.to_f). It is insufficient to append a dot (99.), because numbers are susceptible to method syntax.
• Boolean evaluation of non-boolean data is strict: 0, "" and [] are all evaluated to true. In C, the expression 0 ? 1 : 0 evaluates to 0 (i.e. false). In Ruby, however, it yields 1, as all numbers evaluate to true; only nil and false evaluate to false. A corollary to this rule is that Ruby methods by convention — for example, regular-expression searches — return numbers, strings, lists, or other non-false values on success, but nil on failure (e.g., mismatch). This convention is also used in Smalltalk, where only the special objects true and false can be used in a boolean expression.
• Versions prior to 1.9 lack a character data type (compare to C, which provides type char for characters). This may cause surprises when slicing strings: "abc"[0] yields 97 (an integer, representing the ASCII code of the first character in the string); to obtain "a" use "abc"[0,1] (a substring of length 1) or "abc"[0].chr.

• The notation statement until expression, unlike other languages' equivalent statements (e.g. do { statement } while (not(expression)); in C/C++/...), actually never runs the statement if the expression is already true. This is because statement until expression is actually syntactic sugar over

until expression
  statement
end

，在C/C++中相当于while (not(expression)) statement;就像statement if expression等价于

, the equivalent of which in C/C++ is while (not(expression)) statement; just like statement if expression is an equivalent to

if expression
  statement
end

但是，符号

begin
  statement
end until expression

在 Ruby 中，即使表达式已经为真，该语句实际上也会运行一次.

in Ruby will in fact run the statement once even if the expression is already true.

一些与其他语言明显不同的功能:

Some features which differ notably from other languages:

• 条件表达式的常用运算符，and 和 or，不遵循正常的优先规则:and 不绑定比 或 更紧密.Ruby 还具有表达式运算符 || 和 &&，它们按预期工作.

• The usual operators for conditional expressions, and and or, do not follow the normal rules of precedence: and does not bind tighter than or. Ruby also has expression operators || and && which work as expected.

def 里面的 def 并没有像 Python 程序员所期望的那样:

def inside def doesn't do what a Python programmer might expect:

def a_method
    x = 7
    def print_x; puts x end
    print_x
end

这给出了一个关于 x 未被定义的错误.您需要使用 Proc.

This gives an error about x not being defined. You need to use a Proc.

语言特性

• 如果方法采用多个参数，则省略方法参数周围的括号可能会导致意外结果.Ruby 开发人员表示，在未来的 Ruby 版本中可能不允许省略多参数方法的括号；当前(2007 年 11 月)Ruby 解释器抛出一个警告，鼓励作者不要省略 ()，以避免代码含义模糊.不使用 () 仍然是常见的做法，将 Ruby 用作人类可读的特定领域编程语言本身以及称为 method_missing() 的方法会特别好.

• Omission of parentheses around method arguments may lead to unexpected results if the methods take multiple parameters. The Ruby developers have stated that omission of parentheses on multi-parameter methods may be disallowed in future Ruby versions; the current (November 2007) Ruby interpreter throws a warning which encourages the writer not to omit (), to avoid ambiguous meaning of code. Not using () is still common practice, and can be especially nice to use Ruby as a human readable domain-specific programming language itself, along with the method called method_missing().

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