Using an expression tree to read the name and value of a property. Is there an alternative?

c# expression-trees

Question

Assumptions

Suppose I have a class with a property:

class ClassWithProperty
{
    public string Prop { get; private set; }

    public ClassWithProperty(string prop)
    {
        this.Prop = prop;
    }
}

And now suppose I have created an instance of that class:

var test = new ClassWithProperty("test value");

What I want

I want this printed out to the console:

Prop = 'test value'

Piece of cake! I use this code to produce the wanted output:

Console.WriteLine("Prop = '{1}'", test.Prop);

Problem

I am violating DRY, because "Prop" appears twice in the code above. If I refactor the class and change the name of the property, I also have to change the string literal. There is also a lot of boilerplate code, if I had a class with many properties.

Proposed solution

string result = buildString(() => c.Prop);
Console.WriteLine(result);

Where the buildString method looks like this:

private static string buildString(Expression<Func<string>> expression)
{
    MemberExpression memberExpression = (MemberExpression)expression.Body;
    string propertyName = memberExpression.Member.Name;

    Func<string> compiledFunction = expression.Compile();
    string propertyValue = compiledFunction.Invoke();

    return string.Format("{0} = '{1}'", propertyName, propertyValue);
}

Question

The above solution works fine and I am happy with it, but if there is some more easier and less "scary" way to solve this, that would make me much happier. Is there some easier alternative to achieve the same result with less and simpler code? Maybe something without expression trees?

Edit

Based on Manu's fine idea (see below) I could use this extension method:

static public IEnumerable<string> ListProperties<T>(this T instance)
{
    return instance.GetType().GetProperties()
        .Select(p => string.Format("{0} = '{1}'",
        p.Name, p.GetValue(instance, null)));
}

It's great for getting a string representation for all properties for an instance.

But: From this enumeration, how could I pick type-safely a specific property? Again I would use expression trees ... or am I not seeing the wood for the trees?

Edit 2

Using reflection or expression trees here is a matter of taste.

Luke's idea using projection initializers is just brilliant. From his answer I finally build this extension method (which is basically just a LINQ'd version of his answer):

public static IEnumerable<string> BuildString(this object source)
{
    return from p in source.GetType().GetProperties()
           select string.Format("{0} = '{1}'", p.Name, p.GetValue(source, null));
}

Now a call will look like this:

new { c.Prop }.BuildString().First()

Which looks a bit nicer than the my original call with a lambda (but this is also a matter of taste I guess). Luke's suggestion is however superior to my solution, since it allows specifying as many properties as you like (see below).

Accepted Answer

You could pass an anonymous type to a BuildStrings method, taking advantage of projection initializers to automatically create the names and values of the anonymous type's properties. Inside the method you would use reflection to interrogate those properties.

This would also allow you to pass multiple items if you wished. You could also pass fields and locals as well as properties, because they'd all be projected as properties of the anonymous type that can then be interrogated with GetProperties etc. (Of course, all that the method is actually doing is enumerating all properties of the object that's passed-in. You could pass any type.)

string result = BuildStrings(new { test.Prop }).First();
Console.WriteLine(result);

// or

string foo = "Test";
int bar = 42;

string results = BuildStrings(new { foo, bar, test.Prop });
foreach (string r in results)
{
    Console.WriteLine(r);
}

// ...

public static IEnumerable<string> BuildStrings(object source)
{
    return source.GetType().GetProperties().Select(
        p => string.Format("{0} = '{1}'", p.Name, p.GetValue(source, null)));
}

Expert Answer

I've seen it done with a delegate and IL interrogation, but that isn't exactly simpler. In short, no: there is no infoof in C#. Here's Eric Lippert's take on this: In Foof We Trust: A Dialogue




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