值或 “默认”

Question

可能重复：
Assigning a substitute value in case of nil

在Lua中我使用

x = value or "default_if_value_is_nil" 

（为if value ~= nil then x = value end快捷方式）

我能做类似的事情呃Ruby？

Answer 1

x = value || "default_if_value_is_nil_or_false" 

请注意这里的“或false”，虽然在Lua中也可能也是这样。

Answer 2

实际上，你可以做同样的事情在红宝石

x = nil_value || "default" 

注意，这也适用于任何其他的“falsey”值以及工作

x = false_value || "default" 

Answer 3

x = value or "default_if_value_is_nil" 

是一个完全合法的Ruby声明，但请注意，or在运算符优先级中具有最低优先级之一。也知道在一个Ruby布尔操作中，除了false和nil之外，一切都是真实的，因此，即使值不是零而是假，这个Ruby语句也会回应默认值。

puts '>>> assignment = has a higher priority than or <<<' 
value = 'y' 
x = value or "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = false 
x = value or "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = nil 
x = value or "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

puts '>>> put parenthesis around or expression to have a higher priority than = <<<' 
value = 'y' 
x = (value or "default_if_value_is_nil") 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = false 
x = (value or "default_if_value_is_nil") 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = nil 
x = (value or "default_if_value_is_nil") 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

puts '>>> || has a higher priority than = <<<' 
value = 'y' 
x = value || "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = false 
x = value || "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

value = nil 
x = value || "default_if_value_is_nil" 
print 'value=', value.inspect, ', x=', x.inspect, "\n" 

输出：

>>> assignment = has a higher priority than or <<< 
value="y", x="y" 
value=false, x=false 
value=nil, x=nil 
>>> put parenthesis around or expression to have a higher priority than = <<< 
value="y", x="y" 
value=false, x="default_if_value_is_nil" 
value=nil, x="default_if_value_is_nil" 
>>> || has a higher priority than = <<< 
value="y", x="y" 
value=false, x="default_if_value_is_nil" 
value=nil, x="default_if_value_is_nil"