Question

I have a method that accepts a Expression<Func<T, object>> instance. I want to get at the actual data type being returned by a specific expression instance, rather than object.

I can get it to work for direct property references, so if I pass in the expression x => x.IntegerProperty I can get a Type reference for an integer. This approach requires converting it to a MemberExpression.

However, I can’t get it to work for arbitrary expressions. For instance, if the expression is x => x.IntegerProperty.ToString() I want to get a Type reference for a string. I can’t compile this to a MemberExpression, and if I just .Compile() it and check the return type I get “object”.

How can I look at the specific expression instance and derive the actual return type?

Answer 1

Something like this might do the trick. It probably doesn’t cover every possibility, but it’s a start.

public static Type GetObjectType<T>(Expression<Func<T, object>> expr)
{
    if ((expr.Body.NodeType == ExpressionType.Convert) ||
        (expr.Body.NodeType == ExpressionType.ConvertChecked))
    {
        var unary = expr.Body as UnaryExpression;
        if (unary != null)
            return unary.Operand.Type;
    }
    return expr.Body.Type;
}