Composing invocations with Expression> the same way as Func

Question

Consider a class that can be used as a member of multiple other classes:

class Customer {
    public string FirstName {get;set;}
    public string LastName {get;         


        

Answer 1

Unfortunately, C# does not currently provide a way to compose expressions from Expression<Func<...>> objects. You have to use expression trees, which is quite a bit longer:

static Expression<Func<T,bool>> CheckExpr<T>(Expression<Func<T,Customer>> conv, string first, string last) {
    var arg = Expression.Parameter(typeof(T));
    var get = Expression.Invoke(conv, arg);
    return Expression.Lambda<Func<T,bool>>(
        Expression.MakeBinary(
            ExpressionType.AndAlso
        ,   Expression.MakeBinary(
                ExpressionType.Equal
            ,   Expression.Property(get, nameof(Customer.FirstName))
            ,   Expression.Constant(first)
            )
        ,   Expression.MakeBinary(
                ExpressionType.Equal
            ,   Expression.Property(get, nameof(Customer.LastName))
            ,   Expression.Constant(last)
            )
        )
    ,   arg
    );
}