On Thu, 18 Nov 2010 14:43:17 -0500, spir <[email protected]> wrote:
On Thu, 18 Nov 2010 07:34:01 -0500
"Steven Schveighoffer" <[email protected]> wrote:
4. if you intend on returning a portion of the string, well, currently
you're SOL, but eventually inout will come into play here.
For example, Tango's log package fell under rules 1 and 3 (most of the
time you are creating log objects with string literals, and logging a
message does not save the message anywhere).
Many many cases fell under rule 4, which is one of the main reasons I
gave
up (inout still isn't ready).
I don't understand the issue here. Why don't slices do the job?
It's the source of the problem for which inout was invented to solve. How
do you specify a function that says "I won't molest the data" but returns
a portion of that data?
Simplest example is strstr:
const(char)[] strstr(const(char)[] haystack, const(char)[] needle)
Notice that the return value *must* be const(char)[]. But what if you
have a char[]? All of a sudden, you can't modify that data which was
returned to you. In essence, strstr modified your const contract with
your data. The useful idiom:
str = strstr(str, "hello");
doesn't work, because you can't reassign the data.
A solution is to have 3 overloads, one for each constancy type, but the
mutable version doesn't guarantee it won't modify the data, and you have
to repeat the exact same code. Another solution is to use a template, but
that also has the same problem that it doesn't prevent the mutable version
from modifying the data, plus does not indicate that you can use const
data. In addition, templates cannot be virtual functions.
But inout solves this in a different way that does exactly what we want.
If you have read TDPL, then it should explain how inout is *supposed* to
work, or you can read DIP2
(http://prowiki.org/wiki4d/wiki.cgi?LanguageDevel/DIPs/DIP2). inout was
chosen instead of vconst to allow reusing essentially a dead keyword.
-Steve
