Implementing Linq IENumerable<T> without new() constraint

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Andrus - 22 Mar 2008 09:40 GMT

I noticed that Linq-SQL DataContext ExecuteQuery method does not have new()
constraint:

IEnumerable<TResult> ExecuteQuery( command, ... )

IEnumerable must return object so it must create this object in some way.

Any idea why and how ExecuteQuery<T> can be implemented witout new()
constraint ?

Andrus.

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Jon Skeet [C# MVP] - 22 Mar 2008 11:15 GMT

> I noticed that Linq-SQL DataContext ExecuteQuery method does not have new()
> constraint:
[quoted text clipped - 5 lines]
> Any idea why and how ExecuteQuery<T> can be implemented witout new()
> constraint ?

Given that there's quite a bit of reflection involved (well, at least
initially - it's all compiled into lightweight functions, I believe)
one more bit to create instances isn't that much of a worry.

The new() constraint just lets the compiler use
Activator.CreateInstance, knowing that there'll be a parameterless
constructor avaialable (for classes - it uses initobj for value types).

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Implementing Linq IENumerable<T> without new() constraint

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