Click here to Skip to main content
11,433,170 members (60,787 online)
Click here to Skip to main content
Technical Blog

C# Proposal: Compile Time Static Checking Of Dynamic Objects

, 15 Apr 2010 CPOL
Rate this:
Please Sign up or sign in to vote.
C# Proposal: Compile Time Static Checking Of Dynamic Objects
free hit counters

C# 4.0 introduces a new type: dynamic. dynamic is a static type that bypasses static type checking.

This new type comes in very handy to work with:

Because static type checking is bypassed, this:

dynamic dynamicValue = GetValue();
dynamicValue.Method();

is equivalent to this:

object objectValue = GetValue();
objectValue
    .GetType()
        .InvokeMember(
            "Method",
            BindingFlags.InvokeMethod,
            null,
            objectValue,
            null);

Apart from caching the call site behind the scenes and some dynamic resolution, dynamic only looks better. Any typing error will only be caught at run time.

In fact, if I'm writing the code, I know the contract of what I'm calling. Wouldn't it be nice to have the compiler do some static type checking on the interactions with these dynamic objects?

Imagine that the dynamic object that I'm retrieving from the GetValue method, besides the parameterless method Method also has a string read-only Property property. This means that, from the point of view of the code I'm writing, the contract that the dynamic object returned by GetValue implements is:

string Property { get; }
void Method();

Since it’s a well defined contract, I could write an interface to represent it:

interface IValue
{
    string Property { get; }
    void Method();
}

If dynamic allowed to specify the contract in the form of dynamic(contract), I could write this:

dynamic(IValue) dynamicValue = GetValue();
dynamicValue.Method();

This doesn't mean that the value returned by GetValue has to implement the IValue interface. It just enables the compiler to verify that dynamicValue.Method() is a valid use of dynamicValue and dynamicValue.OtherMethod() isn't.

If the IValue interface already existed for any other reason, this would be fine. But having a type added to an assembly just for compile time usage doesn't seem right. So, dynamic could be another type construct. Something like this:

dynamic DValue
{
    string Property { get; }
    void Method();
}

The code could now be written like this:

DValue dynamicValue = GetValue();
dynamicValue.Method();

The compiler would never generate any IL or metadata for this new type construct. It would only be used, at compile time, for static checking of dynamic objects. As a consequence, it makes no sense to have public accessibility, so it would not be allowed.

Once again, if the IValue interface (or any other type definition) already exists, it can be used in the dynamic type definition:

dynamic DValue : IValue, IEnumerable, SomeClass
{
    string Property { get; }
    void Method();
}

Another added benefit would be IntelliSense.

I've been getting mixed reactions to this proposal. What do you think? Would this be useful?

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Share

About the Author

Paulo Morgado
Software Developer (Senior) Paulo Morgado
Portugal Portugal

Comments and Discussions

 
GeneralGo Pin
Qwertie21-Apr-10 5:59
memberQwertie21-Apr-10 5:59 
GeneralRe: Go Pin
Paulo Morgado23-Apr-10 3:12
memberPaulo Morgado23-Apr-10 3:12 
GeneralRe: Go Pin
Qwertie23-Apr-10 5:24
memberQwertie23-Apr-10 5:24 
GeneralRe: Go Pin
Paulo Morgado23-Apr-10 9:09
memberPaulo Morgado23-Apr-10 9:09 
GeneralRe: Go Pin
Qwertie23-Apr-10 17:07
memberQwertie23-Apr-10 17:07 
GeneralRe: Go Pin
Paulo Morgado25-Apr-10 12:56
memberPaulo Morgado25-Apr-10 12:56 
GeneralRe: Go Pin
Qwertie28-Apr-10 19:10
memberQwertie28-Apr-10 19:10 
GeneralRe: Go Pin
Paulo Morgado28-Apr-10 22:53
memberPaulo Morgado28-Apr-10 22:53 
GeneralWish-list item: narrowly-scoped extension types/functions Pin
supercat915-Apr-10 6:38
membersupercat915-Apr-10 6:38 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
Paulo Morgado15-Apr-10 13:47
memberPaulo Morgado15-Apr-10 13:47 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
supercat916-Apr-10 7:08
membersupercat916-Apr-10 7:08 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
Paulo Morgado16-Apr-10 15:40
memberPaulo Morgado16-Apr-10 15:40 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
supercat917-Apr-10 7:23
membersupercat917-Apr-10 7:23 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
Paulo Morgado17-Apr-10 11:45
memberPaulo Morgado17-Apr-10 11:45 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
supercat919-Apr-10 6:10
membersupercat919-Apr-10 6:10 
GeneralRe: Wish-list item: narrowly-scoped extension types/functions Pin
Paulo Morgado19-Apr-10 14:04
memberPaulo Morgado19-Apr-10 14:04 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web03 | 2.8.150428.2 | Last Updated 15 Apr 2010
Article Copyright 2010 by Paulo Morgado
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid