Semantics of toString

[Steven Schveighoffer]

On Tue, 10 Nov 2009 18:49:54 -0500, Andrei Alexandrescu  
<SeeWebsiteForEmail at erdani.org> wrote:

> I think the best option for toString is to take an output range and  
> write to it. (The sink is a simplified range.)

Bad idea...

A range only makes sense as a struct, not an interface/object.  I'll tell  
you why: performance.

Ranges are special in two respects:

1. They are foreachable.  I think everyone agrees that calling 2 interface  
functions per loop iteration is much lower performing than using opApply,  
which calls one delegate function per loop.  My recommendation -- use  
opApply when dealing with polymorphism.  I don't think there's a way  
around this.
2. They are useful for passing to std.algorithm.  But std.algorithm is  
template-interfaced.  No need for using interfaces because the correct  
instatiation will be chosen.

If you are intending to add a streaming module that uses ranges, would it  
not be templated for the range type as std.algorithm is?  If not, the next  
logical choice is a delegate, which requires no vtable lookup.  Using an  
interface is just asking for a performance penalty for not much gain.

Here's what I mean by not much gain: I would expect a stream range that  
does output to have a method in it for outputting a buffer (I'd laugh at  
you if you wanted to define a stream range that outputs a character at a  
time).  So the difference between:

x.toString(outputRange, format)

and

x.toString(&outputRange.sink, format)

is pretty darn minimal, and if outputRange is an interface or object, this  
saves a virtual call per buffer write.  Plus the second form is more  
universal, you can pass any delegate, and not have to use a range type to  
wrap a delegate.

Don't fall into the "OOP newbie" trap -- where just because you've found a  
new concept that is amazing, you want to use it for everything.  I say  
this because I've seen in the past where someone discovers the power of  
OOP and then wants to use it for everything, when in some cases, it's  
overkill.  Just look at some Java "classes"...

 From another thread:
> Walter does not feel strongly about Phobos.

Huh?  I feel like this sentence doesn't make sense, so maybe there's a  
typo.

-Steve