[FIXED] How to pass 'out' parameter into lambda expression

Issue

I have a method with the following signature:

private PropertyInfo getPropertyForDBField(string dbField, out string prettyName)

In it, I find the associated value prettyName based on the given dbField. I then want to find all properties, if any, that have the name prettyName, so I'm trying to do the following:

IEnumerable<PropertyInfo> matchingProperties =
    getLocalProperties().Where(prop =>
        prop.Name.Equals(prettyName)
    );

However, this gives the following error:

Cannot use ref or out parameter 'prettyName' inside an anonymous method, lambda expression, or query expression

By the point in the method where I'm trying to use prettyName in the Where lambda parameter, prettyName is definitely initialized. I return if prettyName cannot be initialized to a valid value. Is there some trick I could do here to let me use prettyName in the lambda expression?

Edit: I'm using .NET 3.5 if it matters.

Solution

As the compiler error indicates, it isn't allowed to use out or ref parameters inside lambda expressions.

Why not just use a copy? It's not like the lambda wants to mutate the variable anyway, so I don't see a downside.

string prettyNameCopy = prettyName;
var matchingProperties = getLocalProperties()
                        .Where(prop => prop.Name == prettyNameCopy);

Alternatively, you can use a local throughout (to evaluate the appropriate name etc.), and assign the outparameter prettyName just before returning from the method. This will probably be more readable if there isn't significant branching within the method.

Answered By - Ani

Answer Checked By - Gilberto Lyons (PHPFixing Admin)