是否可以在Ruby中使用默认参数定义一个块？

Question

This question处理传递给Ruby块的可选参数。我想知道是否也可以用默认值定义参数，以及它的语法是什么。

乍一看，似乎答案是 “不”：

def call_it &block 
    block.call 
end 

call_it do |x = "foo"| 
    p "Called the block with value #{x}" 
end 

...结果：

my_test.rb:5: syntax error, unexpected '=', expecting '|' 
    call_it do |x = "foo"| 
       ^
my_test.rb:6: syntax error, unexpected tSTRING_BEG, expecting kDO or '{' or '(' 
     p "Called the block with value #{x}" 
     ^
my_test.rb:7: syntax error, unexpected kEND, expecting $end 
    end 
    ^

Answer 1

红宝石1.9允许这样的：

{|a,b=1| ... } 

Answer 2

穷人的默认块参数：

def call_it &block 
    block.call 
end 

call_it do |*args| 
    x = args[0] || "foo" 
    p "Called the block with value #{x}" 
end