Csharp `(bool)value == true` 和 `value == null 之间有区别吗 false ： (bool) value`，其中值是对象类型

发布于04月26日

假设value是object类型，并且永远只有null、true或false的值，以下两个表达式的(A)行为和(B)执行之间是否有任何区别:

// Expression 1
value == null ? false : (bool) value

// Expression 2
(bool?) value == true

推荐答案

如果object value只能包含null、true或false，它们将返回相同的结果.然而，第二个(不出所料)更贵:

表达式1:

IL_0008: ldloc.0
IL_0009: brfalse.s IL_0013

IL_000b: ldloc.0
IL_000c: unbox.any [System.Runtime]System.Boolean
IL_0011: br.s IL_0014

表达式2:

IL_0008: ldloc.0
IL_0009: unbox.any valuetype [System.Runtime]System.Nullable`1<bool>
IL_000e: stloc.2
IL_000f: ldc.i4.1
IL_0010: stloc.3
IL_0011: ldloca.s 2
IL_0013: call instance !0 valuetype [System.Runtime]System.Nullable`1<bool>::GetValueOrDefault()
IL_0018: ldloc.3
IL_0019: ceq
IL_001b: ldloca.s 2
IL_001d: call instance bool valuetype [System.Runtime]System.Nullable`1<bool>::get_HasValue()
IL_0022: and
IL_0023: stloc.1

The value is true version mentioned in the comments is almost the same as 表达式1:

IL_0008: ldloc.0
IL_0009: isinst [System.Runtime]System.Boolean
IL_000e: brfalse.s IL_0018

IL_0010: ldloc.0
IL_0011: unbox.any [System.Runtime]System.Boolean
IL_0016: br.s IL_0019

它还有一个额外的好处，那就是可以容忍value中的其他类型的值，而不仅仅是null、true或false.