Question

I’m searching a list of objects for a certain property. I’m repeating this code for a lot of properties, so I’m trying to make the reading of the property as compact as possible.

Here’s what I currently have:

value = ReadValue(p => p.ProductCatalogId != 0, p => p.ProductCatalogId);

public T ReadValue<T>(Func<MyType, bool> predicate, Func<MyType, T> selector)
{
    return m_settingsPages.Where(predicate).Select(selector).FirstOrDefault();
}

I always compare against the default value for the type, and always for inequality. I would like to remove the predicate argument. Can I use partial application or a similar technique to get rid of the predicate argument?

Pseudo code:

value = ReadFirstValue(p => p.ProductCatalogId);

public T ReadFirstValue<T>(Func<MyType, T> selector) where T : IEquatable<T>
{
    var predicate = selectorToPredicate(selector); //Compare with default(T) for non equality
    return m_settingsPages.Where(predicate).Select(selector).FirstOrDefault();
}

How would selectorToPredicate look and how would I call it?

Answer 1

Sounds like you could do something as simple as:

Func<MyType, bool> SelectorToPredicate<T>(Func<MyType, T> selector)
{
    EqualityComparer<T> comparer = EqualityComparer<T>.Default;
    return x => !comparer.Equals(selector(x), default(T));
}

One thing to note – if your property is a string property, this will return empty strings. Is that what you want?