I just tried the following in a node.js console:
我刚刚在node.js控制台中尝试了以下内容:
> 5 <= "5"
true
Which means that the = part of the <= is treated the same way == is, not ===. Which made me immediately try <== hoping it would do what you would hope it would. But it doesn't exist.
这意味着<=的=部分以相同的方式处理==是,而不是===。这让我立即尝试<==希望它会做你希望它会做的事情。但它不存在。
Then I tried the following:
然后我尝试了以下内容:
> 5 < "6"
true
Then I started to observe even stranger behaviour:
然后我开始观察甚至更奇怪的行为:
> 5 < [6]
true
Which brings up a more important question: are there type-safe equivalents to <, >, <=, and >=?
这提出了一个更重要的问题:<,>,<=和> =是否存在类型安全的等价物?
2 个解决方案
#1
8
No, but it can be handled by correct use of existing language features to type check.
不,但可以通过正确使用现有语言功能来进行类型检查来处理。
Comparison is ideally two state logic. Either a<b or it is not. The problem is that combining type checking with comparison changes two state logic into three state (true/false/incomparable). To return one of three outcomes would no longer be a simple Boolean.
理想情况下,比较是两种状态逻辑。要么 ,要么不是。问题是将类型检查与比较相结合将两个状态逻辑改变为三个状态(真>
A pre-check on types can already be implemented with typeof or instanceOf
可以使用typeof或instanceOf实现对类型的预检查
If comparisons must be type-appropriate, and there is no code written to deal with mismatches, then an error can be thrown to stop execution as in the following example:
如果比较必须是类型相关的,并且没有编写代码来处理不匹配,则可以抛出错误来停止执行,如下例所示:
if (typeof(a) !== typeof(b)) throw "type mismatch in some_function(), types:"+typeof(a)+','+typeof(b);
// now the next operation is "safe"
if (a<=b) { do_something() } else { do_the_other_thing(); }
Later when there is error handling code, you can replace the throw or keep the throw and use try/catch.
稍后当有错误处理代码时,你可以替换throw或保持throw并使用try / catch。
#2
1
No, there's nothing built in to do so.
不,没有内置的东西可以做到这一点。
Consider:
// I invented ~ as the non type coercion operator
5 <~ 6
5 <~ '6'
Both of these return false, but the return values don't really mean the same thing. In the second case, it likely wouldn't have even compared the values.
这两个都返回false,但返回值并不意味着同样的事情。在第二种情况下,它甚至可能不会比较这些值。
#1
8
No, but it can be handled by correct use of existing language features to type check.
不,但可以通过正确使用现有语言功能来进行类型检查来处理。
Comparison is ideally two state logic. Either a<b or it is not. The problem is that combining type checking with comparison changes two state logic into three state (true/false/incomparable). To return one of three outcomes would no longer be a simple Boolean.
理想情况下,比较是两种状态逻辑。要么 ,要么不是。问题是将类型检查与比较相结合将两个状态逻辑改变为三个状态(真>
A pre-check on types can already be implemented with typeof or instanceOf
可以使用typeof或instanceOf实现对类型的预检查
If comparisons must be type-appropriate, and there is no code written to deal with mismatches, then an error can be thrown to stop execution as in the following example:
如果比较必须是类型相关的,并且没有编写代码来处理不匹配,则可以抛出错误来停止执行,如下例所示:
if (typeof(a) !== typeof(b)) throw "type mismatch in some_function(), types:"+typeof(a)+','+typeof(b);
// now the next operation is "safe"
if (a<=b) { do_something() } else { do_the_other_thing(); }
Later when there is error handling code, you can replace the throw or keep the throw and use try/catch.
稍后当有错误处理代码时,你可以替换throw或保持throw并使用try / catch。
#2
1
No, there's nothing built in to do so.
不,没有内置的东西可以做到这一点。
Consider:
// I invented ~ as the non type coercion operator
5 <~ 6
5 <~ '6'
Both of these return false, but the return values don't really mean the same thing. In the second case, it likely wouldn't have even compared the values.
这两个都返回false,但返回值并不意味着同样的事情。在第二种情况下,它甚至可能不会比较这些值。