Are these enumerations code functionally the same?

Question

foreach ( Effect effect in this.Effects.Where ( e => e.IsTransparentEffect && e.HasGPUSupport ) )
 yield return new RealtimeEffect<TransparentEffect> ( effect );

vs

this.Effects.Where ( e => e.IsTransparentEffect && e.HasGPUSupport )
 .Select ( e => new RealtimeEffect<TransparentEffect> ( e ) );

I somehow think the Select would try to gather the results differently than just yielding it like in #1?

Also would there be any performance difference?

Answer 1

It's definitely functionally identical (although I've assumed that the lack of a new keyword in your LINQ example was a typo).

There's a bit of null checking in Select, but that's unlikely to significantly affect performance.

Jon Skeet has a good writeup on his blog here: http://msmvps.com/blogs/jon_skeet/archive/2010/12/23/reimplementing-linq-to-objects-part-3-quot-select-quot-and-a-rename.aspx

• Joan Venge: Thanks added the new keyword.

Answer 2

Both codes will return the same results. Both have deferred execution (i.e. nothing will actually be executed until you start enumerating the result) and stream the results (i.e. not buffered). There shouldn't be a significant performance difference between the two versions