[Ns-developers] A Reason for Slowness of NS3

[Tom Henderson]

George Riley wrote:
> Hi Adrian,
> THanks for posting this.  I recall early on in the design discussions 
> there was
> a lengthy debate about the merits of "pass by value" versus "pass by 
> reference".
> The decision was, I believe, to use "const reference" where possible, 
> precisely
> for the reason you describe below.  The downside is, of course, an 
> additional
> indirection when reading the values passed by reference.  However, we did
> decide pass by reference was generally the best approach.  Clearly, this 
> was
> not always done, but would support your suggested change.  We may want to
> make a more thorough pass looking for any other high-overhead object copies
> for pass by value.
> 
> Tom, feel free to comment.  Is my memory correct on this?
> 

We decided for preferring pass by reference to const when pass-by-value 
semantics are desired.  It hasn't been uniformly followed in the 
codebase; I think we also loosely agreed that we would optimize things 
once we had profiling data to support it.  Looking at this case, it 
seems like a reasonable suggestion (and for other instances where we 
find them at the top of the list).

Tom