Linq Noob, stuck on type inference...

[callingshotgun]

I'm trying to wrap my head around using LINQ and lambda expressions in c# 3.0, and as such I threw together a short (presumably) simple exercise- A general function that will take an IEnumerable and return a concatonation of the string representations of each of the elements contained therein. public String concat(ICollection values ) { return values.Cast().Aggregate((Object x, Object y) => x.ToString() + y.ToString()); } However, when I try to run this little gem, I get the following: "The type arguments for method 'System.Query.Sequence.Aggregate, System.Query.Func<t,t,t>)' cannot be inferred from the usage. Try specifying the type arguments explicitly" Googling revealed that this error is usually the result of saying (x,y) => ... instead of explicitly typing X and Y the way you would when defining the parameters in a method. Makes sense, except that I'm explicitly saying "(Object x, Object y)". Further, when I change all instances of "Object" to "String" (which I don't want to do for the final version, as I want this to work for any type of object), it works without a hitch. I don't understand why that makes a difference, since I'm calling ToString() on the object to get the string out, and "ToString()" works for any object. Is this a failing of the type inference system? Or am I just completely glossing over something? Much appreciated.

[leppie]

public string concat(ICollection values)
{
return (string)values.Cast().Aggregate((x, y) => x.ToString() + y.ToString());
}

xacc.ide - now with TabsToSpaces support
IronScheme - 1.0 alpha 4a out now (29 May 2008)

[callingshotgun]

I'm still getting the "type arguments for method ... cannot be inferred from the usage" error. Even tried throwing gratuitious use of "Object" back in (Object x, Object y). Thanks for the attempt, though.

[leppie]

Member 2148527 wrote:

I'm still getting the "type arguments for method ... cannot be inferred from the usage" error. Even tried throwing gratuitious use of "Object" back in (Object x, Object y). Thanks for the attempt, though.

Erm, the code as I pasted I compiled, so either you are missing something, or you are compiling in VS2005 maybe (or using the C# 2.0 compiler?)!

xacc.ide - now with TabsToSpaces support
IronScheme - 1.0 alpha 4a out now (29 May 2008)

[callingshotgun]

My mistake- I was using a "linq playground" project I'd initially created in VS2005. Moving to 2008 apparently didn't update all the references, so it was still trying to compile down to C# 2.0. Changed the LINQ references to point to 3.5 (instead of the preview release that you could download for 2.0), and changed the "target" to .NET framework 3.5, and it works perfectly now. Sorry for the confusion, and thanks for the help!