[prospero]

I'm not the OP, but here are some compiler features missing from C# 2.0 that would have prevented a LINQ-type library: lambda expressions, implicit types, and anonymous types.

None of these required modification to the runtime, they were purely compiler features. And, as pointed out, they were features only Microsoft had the ability to implement.

[mquander]

Strictly speaking, none of those features were necessary to implement LINQ. Anonymous functions were already possible in C# 2.0 with the ugly delegate syntax. Type inference saves a lot of keystrokes, and anonymous types save big families of generic tuple types, but you could do without -- hell, people write functional Java.

(A better comparison would be to look at LINQ-to-SQL specifically; that would not be possible in any sense without the expression tree libraries and compiler support introduced in C# 3.0, since there was no way to "quote" a C# expression and look into it. That's much closer to the mark here.)

However, I agree with you in spirit. A big enough quantitative difference becomes a qualitative one; nobody would actually want to use LINQ+C#2. And likewise, few people want to write small-scale DSLs in C#.

[DougBTX]

Well, your argument is tiptoeing down a very narrow path based on the definition of "necessary". Here's what Eric Lippert has to say about which features were necessary for LINQ: http://blogs.msdn.com/b/ericlippert/archive/2009/10/05/why-n...

[prospero]

Yes, you're right. Expression trees are especially interesting from an integrated DSL perspective, since you can do ridiculous things like turn lambda expressions into a syntax for hashes and so on. I omitted them because I believe that really did require a runtime modification to support.

But I would argue that since DSLs are all about affordances, it's not sufficient to say that similar functionality would be "possible". If the new approach doesn't represent significant semantic compression (which your hypothetical LINQ+C#2 would not), no one will use it. By that measure, the syntactic sugar added to C# 3.0 was absolutely a necessary precondition for LINQ.

[rayvega]

LinqBridge allows support for Linq to run on .NET 2.0. The description of how it works might provide some insight:

http://www.albahari.com/nutshell/linqbridge.aspx

[prospero]

That requires the .NET 3.0 compiler to work, which was my point: LINQ is largely a compile-time feature.

[gnaritas]

No, the features that were used to build LINQ were added to C#. LINQ was then built using them, and those same features are available to you to build anything similar.