output ranges: by ref or by value?

[Michel Fortin]

On 2010-01-01 14:10:40 -0500, Jason House <jason.james.house at gmail.com> said:

>> With save() in tow, class ranges and struct ranges can be used the same
>> way. True, if someone forgets to say
>> 
>> auto copy = r.save();
>> 
>> and instead says:
>> 
>> auto copy = r;
>> 
>> the behavior will indeed be different for class ranges and struct ranges.
> 
> Or if they completely forgot that bit of convention and omit creating a 
> variable called save... Also, doesn't use of save degrade performance 
> for structs? Or does the inliner/optimizer remove the copy variable 
> altogether?

I don't think this will be a problem for the optimizer.

But I say dump save(): it's more trouble than it's worth.

I'm sure it will be a problem for most programmers, as most will learn 
and test algorithms with arrays and struct ranges and not classes. 
"save()" is a detail too easy to miss. The benefit of supporting 
classes by asking everyone to remember adding save() seems tiny 
considering you can easily create a struct wrapper if you really need 
your range to be a class.

I know that the struct wrapper would probably force more copies of a 
range than necessary. But there are many ways this could be alleviated. 
For instance, the struct wrapper could use copy-on-write with a 
reference counter to detect when a copy is necessary. So while it'd be 
a little harder to design a range from a class, it'd be easier for 
everyone to use ranges correctly.

-- 
Michel Fortin
michel.fortin at michelf.com
http://michelf.com/