使用`in`关键字导致“E1012常数表达式违反子范围”在德尔福 [英] Using the `in` keyword causes "E1012 Constant expression violates subrange bounds" in Delphi

问题描述

我在Delphi代码中遇到了一些非常不寻常的行为。当使用关键字中的来检查项目是否在常量数组中时，我收到以下编译错误：

E1012常数表达式违反子范围

常量定义如下：

 类型TSomeEnum =（seFoo = 1000，
 seBar = 2000，
 seBoo = 3000，
 seFar = 
 seFooBar = 5000，
 seBooFar = 6000，
 seLow = 1000，
 seHigh = 6000，
 seCount = 6）; 
  

失败的行如下：

 如果[seFoo，seFar，seFooBar]中的someObj.someProperty然后
 ... 
  

虽然我了解错误背后的原因在另一个问题发布在这里，在使用变量的编译时没有完成对整数数组进行检查的边界，看起来很奇怪，我得到相同一个常数数组的问题，这绝对是在边界内。

现在，我用一个（大得多）的语句替换了这个行，它包含或子句。但是这显然不是很理想。任何人都可以看出为什么我得到这个问题？

解决方案

有关 设置 说：

基类型可以不超过256个可能的值，其序数必须在0到255之间。

所以即使你可以有任何值的枚举，如果[a，b，c] 语句中的xx将在这里失败，那么一个大于255的值。

改用case语句：

  case xx 
a，b，c：// make something 
 
 end; 
  

I've come across some rather unusual behaviour in a bit of Delphi code. When using the in keyword to check if an item is in a constant array, I get the following compilation error:

E1012 Constant expression violates subrange bounds

The constants are defined as follows:

type TSomeEnum = (seFoo = 1000,
                  seBar = 2000,
                  seBoo = 3000,
                  seFar = 4000,
                  seFooBar = 5000,
                  seBooFar = 6000,
                  seLow = 1000,
                  seHigh = 6000,
                  seCount = 6);

The line that is failing is the following:

if someObj.someProperty in [seFoo, seFar, seFooBar] then
...

Whilst I understand the reasoning behind the error showing in another question posted here, where bounds checking on integer arrays wasn't done at compile time when using a variable, it seems odd that I'm getting the same problem with a constant array which is most certainly within bounds.

For now, I've replaced the line with a (much larger) statement comprising of or clauses. However, this is clearly not ideal. Can anyone shed any light on why I'm getting this problem?

解决方案

Documentation about Sets says :

The base type can have no more than 256 possible values, and their ordinalities must fall between 0 and 255.

So even if you can have enums of any value, the if xx in [a,b,c] statement will fail here, since a set cannot hold a value larger than 255.

Use a case statement instead:

case xx of
  a,b,c : // Make something 

end;

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