• Joseph Rushton Wakeling via Digitalmars-d-learn (3/3) Dec 28 2014 A question that suddenly occurred to me, and I realized I didn't know th...
• Tobias Pankrath (6/10) Dec 28 2014 To allow slicing for types that don't have a length property but
• Jonathan M Davis via Digitalmars-d-learn (10/21) Dec 28 2014 Indeed, though there's definitely been discussion of making it so that
• Joseph Rushton Wakeling via Digitalmars-d-learn (4/8) Dec 28 2014 Ah, clear. Thanks very much. (Must remember to look into the multi-dim...

Joseph Rushton Wakeling via Digitalmars-d-learn writes:

A question that suddenly occurred to me, and I realized I didn't know the
answer.

Why is it necessary/desirable to define separate .length and .opDollar methods 
for custom types?

"Tobias Pankrath" <tobias pankrath.net> writes:

On Sunday, 28 December 2014 at 18:12:42 UTC, Joseph Rushton
Wakeling via Digitalmars-d-learn wrote:
 A question that suddenly occurred to me, and I realized I 
 didn't know the answer.

 Why is it necessary/desirable to define separate .length and 
 .opDollar methods for custom types?

To allow slicing for types that don't have a length property but
are terminated by a sentinel value, like null terminated strings
or single linked lists.

It's usefull for multi-dimensional containers as well.

Jonathan M Davis via Digitalmars-d-learn writes:

On Sunday, December 28, 2014 18:21:41 Tobias Pankrath via Digitalmars-d-learn
wrote:
 On Sunday, 28 December 2014 at 18:12:42 UTC, Joseph Rushton
 Wakeling via Digitalmars-d-learn wrote:
 A question that suddenly occurred to me, and I realized I
 didn't know the answer.

 Why is it necessary/desirable to define separate .length and
 .opDollar methods for custom types?

 To allow slicing for types that don't have a length property but
 are terminated by a sentinel value, like null terminated strings
 or single linked lists.

 It's usefull for multi-dimensional containers as well.

Indeed, though there's definitely been discussion of making it so that
opDollar is not necessary under at least some circumstances when length is
defined:

https://issues.dlang.org/show_bug.cgi?id=7177

But unfortunately, the nitty gritty details are just complicated enough that
it hasn't happened yet. I really wish that it would though so that we can
require that random access ranges define opDollar and then actually be able
to use opDollar for random access ranges in generic code.

- Jonathan M Davis

Joseph Rushton Wakeling via Digitalmars-d-learn writes:

On 28/12/14 19:21, Tobias Pankrath via Digitalmars-d-learn wrote:
 To allow slicing for types that don't have a length property but
 are terminated by a sentinel value, like null terminated strings
 or single linked lists.

 It's usefull for multi-dimensional containers as well.

Ah, clear.  Thanks very much.  (Must remember to look into the
multi-dimensional 
container issue in more detail, that looks like something worth understanding
in 
depth.)