Question

Currently i am creating an extension method that accepts parameters. Using the below example, how could one convert this using lambda expressions?

public static decimal ChangePercentage(this IEnumerable<Trade> trades, DateTime startDate, DateTime endDate)
{
    var query = from trade in trades
                where trade.TradeTime >= startDate
                where trade.TradeTime <= endDate
                orderby trade.TradeTime descending
                select trade;
    return (query.First().Value - query.Last().Value) / query.First().Value * 100;
}

What are the pro/cons using lambda vs normal method parameters?

Thanks

Answer 1

One way you could change the sample to use lambda expressions is to use a filter.

public static decimal ChangePercentage(this IEnumerable<Trade> trades, 
                                       Func<Trade,bool> pred)
        {
            var query = from trade in trades
                        where pred(trade);
                        orderby trade.TradeTime descending
                        select trade;
            return (query.First().Value - query.Last().Value) / query.First().Value * 100;
        }

    someTrades.ChangePercentage(x => x.TradeDate >= startDate && x.TradeTime <= endDate);

The biggest pro this gives you is flexbility. Instead of having a method which does date based filtering for calculation. You have a method with a flexible filter method for calculating percentages.