使用泛型返回扩展方法

Question

Is it possible to return a generic type using extension methods ?

For example, I have the following method:

// Convenience method to obtain a field within a row (as a double type) 
public static double GetDouble(this DataRow row, string field) {
    if (row != null && row.Table.Columns.Contains(field))
    {
        object value = row[field];
        if (value != null && value != DBNull.Value)
            return Convert.ToDouble(value);
    }
    return 0;
}

This is currently used as follows:

double value = row.GetDouble("tangible-equity");

but I would like to use the following code:

double value = row.Get<double>("tangible-equity");

Is this possible and if so, what would the method look like?

Answer 1

How about this one:

    public static T Get<T>(this DataRow row, string field) where T: IConvertible 
    {
        if (row != null && row.Table.Columns.Contains(field))
        {
            object value = row[field];
            if (value != null && value != DBNull.Value)
                return (T)Convert.ChangeType(value, typeof(T));
        }
        return default(T);
    }

Convert.ChangeType is much more flexible handling conversions as opposed to just casting. This pretty much reflects your original code, just generic.

Answer 2

It is possible. It could be something like the following:

// Convenience method to obtain a field within a row (as a T type) 
public static T Get<T>(this DataRow row, string field) {
    if (row != null && row.Table.Columns.Contains(field))
    {
        object value = row[field];
        if (value != null && value != DBNull.Value)
            return (T)value;
    }
    return default(T);
}

Answer 3

The DataRow has an extension method called Field that will do very much what you are trying to do. I'm not exactly sure how it will behave with a null value on a double (I know it will handle nullable types). This may not be exactly what you are looking for, but is worth a look.

double value = row.Field<double>("tangible-equity");