Create LINQ intermediate variable the way .Select it does

I created the following extension:

public static class StackTraceExtensions
{
    public static string Callers(this StackTrace trace)
    {
        return string.Join(" < ", trace.GetFrames().Select(sf => sf.GetMethod().DeclaringType.Name + "." + sf.GetMethod().Name));
    }
}

but calling GetMethod() every time isn’t a good solution. I looked for some way to create an intermediate variable the way the LINQ .Select function it does.

.Select is available only for IEnumerable and is intended for multiple values, therefore I developed yet another extension, this time for any object:

public static class ObjectExtensions
{
    public static TResult Self<TSource, TResult>(this TSource source, Func<TSource, TResult> selector) => selector(source);
}

This extension could be used as follows:

public static class StackTraceExtensions
{
    public static string Callers(this StackTrace trace)
    {
        return string.Join(" < ", trace.GetFrames().Select(sf => sf.GetMethod().Self(mb => $"{mb.DeclaringType.Name}.{mb.Name}")));
    }
}

It allows me to deal here with the intermediate mb "variable".

Is there some standard extension that does the same so I don’t need to create my own?

>Solution :

You can first select the method and then use it in a subsequent Select:

return string.Join(" < ", trace.GetFrames()
    .Select(sf => sf.GetMethod())
    .Select(m => $"{m.DeclaringType.Name}.{m.Name}"));