Hi,
You are interpreting it correctly. I don't have time at the moment to
write up an example where multiple independent lifetime parameters would
be required, but it is certainly true that this would be very unusual.
In any case, I have several examples that require two lifetime
parameters to be done most naturally, but none that require three, and
I'll try to write them up (perhaps in a blog post) over the next few
days. The main thing is that, today, we are limited to one---it is
*almost* always enough, but not quite, which is why I'd like to
generalize to multiple for advanced uses.
Niko
James Boyden wrote:
Upon re-reading my message, I realised I could have explained
my source of confusion better. So, if I may clarify my question:
If `B<'c, 'd, 'e>` is intended to be equivalent to what's currently
written `B/c/d/e`, does this mean that struct B would be declared
something like this:
struct B<'X, 'Y, 'Z>
?
That is, a template with 3 independent lifetime parameters?
In which case, what would be a hypothetical example which might
require 3 lifetime parameters?
I can understand the purpose of a single lifetime parameter that
corresponds to the lifetime of the struct instance, such as in the
example:
struct StringReader<&self>
but I can't think of an example involving 3 independent lifetime
parameters at the struct definition level.
Or have I misunderstood what `B<'c, 'd, 'e>` is meant to mean?
Thanks,
jb
On Sun, Jan 27, 2013 at 1:26 AM, James Boyden<[email protected]> wrote:
On Thu, Jan 24, 2013 at 10:00 AM, Niko Matsakis<[email protected]> wrote:
The slashes are visually hard to parse, I think everyone agrees. Imagine
this: `&a/B/c/d/e`. That would be a legal type under that proposal and I
think it's pretty darn confusing vs `&'a B<'c, 'd, 'e>`
Hi,
This is a very interesting discussion. I'm also new to the concept of
lifetime parameters, but as a frustrated longtime C++ programmer, I
appreciate the concept.
Unfortunately, having studied these pages:
http://static.rust-lang.org/doc/tutorial-borrowed-ptr.html#returning-borrowed-pointers
http://static.rust-lang.org/doc/tutorial-borrowed-ptr.html#named-lifetimes
http://smallcultfollowing.com/babysteps/blog/2012/12/30/lifetime-notation/
http://smallcultfollowing.com/babysteps/blog/2013/01/15/lifetime-notation-redux/
I still find myself no closer to understanding what `B<'c, 'd, 'e>`
would practically mean, nor how it would be realistically used.
Would you be able to clarify?
Thanks,
jb
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