有反正我可以使用，如果其他内部红宝石case..end

Question

case search_term 
when 'a' 
    ptr = 0 
when 'b' 
    ptr = 1 
when 'c' 
    ptr = 2 
else 
    ptr = 99 
end 

if location = 'xyz' and search_term = 'c' 
ptr = 0 
end 

有什么办法可以包括如果上面的情况说明？

Answer 1

ptr = case search_term 
when 'a' 
    0 
when 'b' 
    1 
when 'c' 
    if location == 'xyz' then #note the == 
    0 
    else 
    2 
    end 
else 
    99 
end 

Answer 2

case构造通常不用于复杂逻辑。虽然你可以找到一个可行的解决方案（比如@steenslag的答案），但随着条件变得更加复杂，这条路径会导致麻烦。一个case声明与三个或四个分支是可行的，但已经有点代码味道。不止这成为问题。将条件放入when分支会使问题复杂化。

你可能会考虑使用小方法将事情分解成单独的职责。这将使您的代码在未来更易于理解，扩展和修改。

def pointer # Ruby convention is to use real words where practical 
    special_condition? ? 0 : pointer_base 
end 

def special_condition? 
    location == 'xyz' && search_term == 'c' 
end 

def pointer_base 
    search_term_map[search_term] || 99 
end 

def search_term_map 
    ('a'..'c').zip(0..2).to_h # This could just as easily be ('a'..'z').zip(0..25).to_h 
end 

Answer 3

您可以使用三元运算符的时候，子句中：

case search_term 
when 'a' 
    ptr = 0 
when 'b' 
    ptr = 1 
when 'c' 
    ptr = location == 'xyz' ? 0 : 2 
else 
    ptr = 99 
end 

两个备注：

• 见==比较（=是一个赋值）

Answer 4

这将是另一种可能性：

ptr = (location == 'xyz') ? 0 : 2 

括号不是必需的，但我发现它更具可读性。

Answer 5

如果我写它简洁地我会用：是不是真的建议

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     location == 'xyz' ? 0 : 2 
     else 
     99 
     end 

三元陈述尽管许多语言允许他们，主要是因为太多的人不知道如何使用它们，或安全/可维护地使用它们。

或者它可以写成：

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 

如果你真的想要得到乐趣，你可以利用Hash.new的恢复默认值的功能：

​​

测试他们：

search_term = 'a' 
location = 'xyz' 

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 
ptr # => 0 

Hash.new(99).merge(
    'a' => 0, 
    'b' => 1, 
    'c' => location == 'xyz' ? 0 : 2 
)[search_term] # => 0 

---

search_term = 'b' 
location = 'xyz' 

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 
ptr # => 1 

Hash.new(99).merge(
    'a' => 0, 
    'b' => 1, 
    'c' => location == 'xyz' ? 0 : 2 
)[search_term] # => 1 

---

search_term = 'c' 
location = 'xyz' 

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 
ptr # => 0 

Hash.new(99).merge(
    'a' => 0, 
    'b' => 1, 
    'c' => location == 'xyz' ? 0 : 2 
)[search_term] # => 0 

---

search_term = 'c' 
location = 'abc' 

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 
ptr # => 2 

Hash.new(99).merge(
    'a' => 0, 
    'b' => 1, 
    'c' => location == 'xyz' ? 0 : 2 
)[search_term] # => 2 

---

search_term = 'z' 
location = 'xyz' 

ptr = case search_term 
     when 'a' 
     0 
     when 'b' 
     1 
     when 'c' 
     if location == 'xyz' 
      0 
     else 
      2 
     end 
     else 
     99 
     end 
ptr # => 99 

Hash.new(99).merge(
    'a' => 0, 
    'b' => 1, 
    'c' => location == 'xyz' ? 0 : 2 
)[search_term] # => 99 

定义散列上飞是OK，如果你在不长的循环或迭代很多值的search_term或有没有很多键/值对被合并。通常我会用第一种风格来定义它。