问题描述
有人可以解释为什么我不能在C#属性中使用const Int32吗?
Can anybody explain why I can't use a const Int32 in an C# attribute?
示例:
private const Int32 testValue = 123;
[Description("Test: " + testValue)]
public string Test { get; set; }
使编译器说:
为什么?
推荐答案
由于错误状态,属性参数必须是恒定表达式。
As the error states, an attribute argument must be a constant expression.
连接字符串和整数不是常量表达式。
Concatenating a string and an integer is not a constant expression.
因此,如果您通过 Test: + 123
,它将给出相同的错误。
另一方面,如果将 testValue
更改为字符串,它将进行编译。
Thus, if you pass "Test: " + 123
directly, it will give the same error.On the other hand, if you change testValue
to a string, it will compile.
常量表达式的规则规定,只要两个操作数本身都是常量表达式,常量表达式就可以包含算术运算符。
The rules for constant expressions state that a constant expression can contain arithmetic operators, provided that both operands are themselves constant expressions.
因此, A + B
仍为常数。
但是, A + 1
使用 string运算符+(string x,object y);
,其中将整数操作数装箱到对象上。 >
常量表达式规则明确指出
However, "A" + 1
uses the string operator +(string x, object y);
, in which the integer operand is boxed to an object.
The constant-expression rules explicitly state that
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