I'm building a LINQ expression tree but it won't compile because allegedly the local variable $var1
is out of scope:
variable '' of type 'System.Object' referenced from scope '', but it is not defined
This is the expression tree:
.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
}
The following code is responsible for building the tree. It is part of something larger, therefore I don't expect its purpose to be perfectly clear from this example.
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()();
So the question is: how do I get the local variable into scope so that the expression compiles succesfully?
Your'e adding the Expression.Variable
to the list of "normal" expressions in the block - you should use the overload which specifies the variables do declare for the block separately:
Expression finalExpression = Expression.Block(new[] { resultVariable },
expressions);
(And remove the call to expressions.Add(resultVariable);
)