Ruby中的“：*”（冒号星）是什么意思？

Looking up how to calculate the factorial of a number I came across this code:

查看如何计算数字的阶乘，我遇到了这段代码：

(1..5).inject(:*) || 1 # => 120

What is the (:*) || 1 doing?

什么是（：*）|| 1做什么？

How does it compare to this line of code (1..5).inject(1) { |x, y| x * y } # => 120, which uses .inject to achieve similar functionality?

它与这行代码（1..5）相比如何.inject（1）{| x，y | x * y}＃=> 120，它使用.inject来实现类似的功能？

3 个解决方案

#1

Colon-star in itself doesn't mean anything in Ruby. It's just a symbol and you can pass a symbol to the inject method of an enumerable. That symbol names a method or operator to be used on the elements of the enumerable.

冒号星本身并不代表Ruby中的任何东西。它只是一个符号，您可以将符号传递给可枚举的注入方法。该符号命名要在可枚举元素上使用的方法或运算符。

So e.g.:

例如：

(1..5).inject(:*) #=> 1 * 2 * 3 * 4 * 5 = 120
(1..5).inject(:+) #=> 1 + 2 + 3 + 4 + 5 = 15

The || 1 part means that if inject returns a falsey value, 1 is used instead. (Which in your example will never happen.)

|| 1部分表示如果inject返回falsey值，则使用1。（在你的例子中哪个永远不会发生。）

#2

test.rb:

test.rb：

def do_stuff(binary_function)
  2.send(binary_function, 3)
end

p do_stuff(:+)
p do_stuff(:*)

$ ruby test.rb

5

五

6

6

If you pass a method name as a symbol, it can be called via send. This is what inject and friends are doing.

如果将方法名称作为符号传递，则可以通过send调用它。这是注入和朋友正在做的事情。

About the || part, in case the left hand side returns nil or false, lhs || 1 will return 1

关于||部分，如果左侧返回nil或false，lhs || 1将返回1

#3

It's absolutely equal. You may use each way, up to your taste.

这绝对是平等的。您可以根据自己的喜好使用各种方式。

#1