Ruby：隐式散列的规则 [英] Ruby: rules for implicit hashes

问题描述

为什么第二个输出只显示 Array 中的一个元素？它还是 Array 还是 Hash 已经？

Why second output shows me only one element of Array? Is it still Array or Hash already?

def printArray(arr)
    arr.each { | j |
        k, v = j.first
        printf("%s %s %s \n", k, v, j)
    }
end

print "Array 1\n"
printArray( [
                {kk: { 'k1' => 'v1' }},
                {kk: { 'k2' => 'v2' }},
                {kk: { 'k3' => 'v3' }},
            ])


print "Array 2\n"
printArray( [
                kk: { 'k1' => 'v1' },
                kk: { 'k2' => 'v2' },
                kk: { 'k3' => 'v3' },
            ])

exit

# Output:
#
# Array 1
# kk {"k1"=>"v1"} {:kk=>{"k1"=>"v1"}} 
# kk {"k2"=>"v2"} {:kk=>{"k2"=>"v2"}} 
# kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}} 
# Array 2
# kk {"k3"=>"v3"} {:kk=>{"k3"=>"v3"}}

推荐答案

Ruby将第二个示例解释为具有单个哈希一个它的元素（大括号暗含）。这相当于：

Ruby interpreted the second example as an array with a single hash as its element (the curly braces are implied). It is equivalent to this:

[{ kk: { 'k1' => 'v1' }, kk: { 'k2' => 'v2' }, kk: { 'k3' => 'v3' }}]

只有最后一个'kk'是因为散列不能有重复键;只有最后一个支持。

Only the last 'kk' is shown because hashes can't have duplicate keys; only the last one sticks.

如果您想要一个包含多个哈希值的数组作为元素，您需要使用第一个示例中的语法。

If you want an array with multiple hashes as elements, you need to use the syntax like on your first example.

更多ruby暗示哈希开始的例子：

More examples on which ruby implies a hash start:

# Only argument on method calls
def only_arg(obj)
  puts obj.class
end

only_arg(bar: "baz")  # => Hash

# Which is equivalent to:
only_arg({bar: "baz"}) # => Hash


# Last argument on method calls
def last_arg(ignored, obj)
  puts obj.class
end

last_arg("ignored", bar: "baz") # => Hash

# Which is equivalent to:
last_arg("ignored", { bar: "baz" }) # => Hash


# Last element on an array
def last_on_array(arr)
  puts arr.last.class
end

last_on_array(["something", "something", bar: "baz"]) # => Hash

# Which is equivalent to:
last_on_array(["something", "something", { bar: "baz" }]) # => Hash

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