C# in Depth

Delegation as the new inheritance355associated with dynamic languages. In particular, the implicitly typed local variables andarrays, extra type inference capabilities for generic methods, extension methods, andbetter initialization structures are all things that in some ways look like they belong indynamic languages.While C# itself is currently statically typed, the Dynamic Language Runtime (DLR)will bring dynamic languages to .NET. Integration between static languages anddynamic ones such as IronRuby and IronPython should therefore be relativelystraightforward—this will allow projects to pick which areas they want to write dynamically,and which are better kept statically typed.Should C# become dynamic in the future? Given recent blog posts from the C#team, it seems likely that C# 4 will allow dynamic lookup in clearly marked sections ofcode. Calling code dynamically isn’t the same as responding to calls dynamically, however—andit’s possible that C# will remain statically typed at that level. That doesn’tmean there can’t be a language that is like C# in many ways but dynamic, in the sameway that Groovy is like Java in many ways but with some extra features and dynamicexecution. It should be noted that Visual Basic already allows for optionally dynamiclookups, just by turning Option Strict on and off. In the meantime, we should begrateful for the influence of dynamic languages in making C# 3 a lot more expressive,allowing us to state our intentions without as much fluff surrounding the really usefulbits of code.The changes to C# don’t just affect how our source code looks in plain text terms,however. They should also make us reconsider the structure of our programs, allowingdesigns to make much greater use of delegates without fear of forcing thousands ofone-line methods on users.13.2 Delegation as the new inheritanceThere are many situations where inheritance is currently used to alter the behavior ofa component in just one or two ways—and they’re often ways that aren’t so muchinherent in the component itself as in how it interacts with the world around it.Take a data grid, for example. A grid may use inheritance (possibly of a typerelated to a specific row or column) to determine how data should be formatted. Inmany ways, this is absolutely right—you can build up a flexible design that allows forall kinds of different values to be displayed, possibly including images, buttons,embedded tables, and the like. The vast majority of read-only data is likely to consist ofsome plain text, however. Now, we could have a TextDataColumn type with an abstractFormatData method, and derive from that in order to format dates, plain strings,numbers, and all kinds of other data in whatever way we want.Alternatively, we could allow the user to specify the formatting by way of a delegate,which simply converts the appropriate data type to a string. With C# 3’s lambda expressions,this makes it easy to provide a custom display of the data. Of course, you may wellwant to provide easy ways of handling common cases—but delegates are immutable in.NET, so simple “constant” delegates for frequently used types can fill this need neatly.Licensed to Rhona Hadida