我正在构建一个LINQ表达式树,但由于据称本地变量$var1
超出了范围而无法编译:
变量“”类型为“System.Object”,在作用域“”中引用,但未定义
这是表达式树:
.Block() {
$var1;
.If ($n.Property1 == null) {
.Block() {
$var1 = null;
.Return #Label1 { }
}
} .Else {
.Default(System.Void)
};
$var1 = (System.Object)($n.Property1).Length;
.Label
.LabelTarget #Label1:;
$var1
}
以下代码负责构建树。它是更大的东西的一部分,因此我不希望从这个示例中完全清楚其目的。MemberExpression sourceExpression = ...;
List<Expression> expressions = new List<Expression>();
LabelTarget returnTarget = Expression.Label();
ParameterExpression resultVariable = Expression.Variable(typeof(object));
expressions.Add(resultVariable);
expressions.Add(
Expression.IfThen(
Expression.Equal(sourceExpression, Expression.Constant(null)),
Expression.Block(
Expression.Assign(resultVariable, Expression.Constant(null)),
Expression.Return(returnTarget))));
expressions.Add(
Expression.Assign(
resultVariable,
Expression.Convert(sourceExpression, typeof(object))));
expressions.Add(Expression.Label(returnTarget));
expressions.Add(resultVariable);
Expression finalExpression = Expression.Block(expressions);
object result = Expression.Lambda<Func<object>>(finalExpression).Compile()();
所以问题是:我如何使局部变量进入作用域,以便表达式可以成功编译?