ruby-on-rails - Ruby splat and << operators

Question

I want to do this:

a << *b

but this happens in irb:

1.9.3p327 :020 > a
 => [1, 2, 3, 4] 
1.9.3p327 :021 > b
 => [5, 6, 7] 
1.9.3p327 :022 > a << *b
SyntaxError: (irb):22: syntax error, unexpected tSTAR
a << *b
      ^

Am I missing something?

Answer 1

我已经评论了它，现在添加它来回答;-)

a += b 会做你的工作

Answer 2

尝试这个：

 a.concat(b)

它将输出：

=> [1, 2, 3, 4, 5, 6, 7] 

Answer 3

看看这里的原因：

 a = [1, 2, 3, 4] 
 b = [5, 6, 7] 
 p a.<<(*b)
 # ~> -:3:in `<<': wrong number of arguments (3 for 1) (ArgumentError)
 # ~>  from -:3:in `<main>'

<<方法只需要一个参数。所以现在如下所示 splat( *) 是一个运算符，它将创建，不期望5,6,7哪个方法，而是只需要一个对象。因此 Ruby 的设计之前<<不允许。*b

 a = [1, 2, 3, 4] 
 b = [5, 6, 7] 
 p a << *
 # ~> -:3: syntax error, unexpected *

 a = [1, 2, 3, 4] 
 b = [5, 6, 7] 
 p a << *b
 # ~> -:3: syntax error, unexpected *
 # ~> p a << *b
 # ~>         ^

这就是为什么 2 个合法错误：

• 参数数量错误（1 为 3）（ArgumentError）

• 语法错误，意外 *

也许你可以使用 -

 a = [1, 2, 3, 4] 
 b = [5, 6, 7] 
 p a.push(*b)
 # >> [1, 2, 3, 4, 5, 6, 7]

Answer 4

Given

a = [1, 2, 3, 4]
b = [5, 6, 7]

The solution you want is

a.concat b
# => [1, 2, 3, 4, 5, 6, 7]

However, you might find this a little interesting

b.each &a.method(:<<)
a
# => [1, 2, 3, 4, 5, 6, 7]

This says "call method a#<< on each element in b"

Equivalent to

b.each &a.method(:push)
a
# => [1, 2, 3, 4, 5, 6, 7]

Answer 5

检查类型签名：ary << obj → ary。它只需要一个参数。尝试：a.push(*b) (push(obj, ... ) → ary)