El 28/11/2010 20:37, Jonathan M Davis escribió:
On Sunday 28 November 2010 11:37:26 Tom wrote:
El 28/11/2010 04:11, Jonathan M Davis escribió:
On Saturday 27 November 2010 22:48:28 Tom wrote:
Hi,
I wonder how to solve this kind of stuff...
void foo(string[] sarray) {
// do something with sarray
}
void bar(int[] iarray) {
auto sarray = map!(to!string)(iarray);
foo(sarray);
}
And get...
foo (string[] sarray) is not callable using argument types
(Map!(to,int[]))
What should I do? Is there some way to get the original array type?
Many functions in std.algorithm return range types specific to that
function. A number of these do lazy evaluation, so the actual work of
the function is done when iterating over the resulting range. map
happens to be one of those.
For all such functions, if you want an array out of the deal, what you do
is pass the result to std.array.array(). That will take an arbitrary
range and return its contents as an array - which also forces the
processing of the range in the case of lazy evaluation like you get with
map. So, if you want to delay the evaluation at all, or if it's really
only go to make sense that some of the range be processed, you may not
want to actually put it in an array. The combination of auto and
templates can avoid making you actually turn it into an array in many
cases. But if you do want an array, std.array.array() is what you're
looking for.
- Jonathan M Davis
Thank you very much.
Is there some documentation (besides digitalmars ddoc's, which I find
very chaotic for a starting point) that explains these structures, when
to use them (instead of arrays), and how they interact with arrays? It's
very difficult to find that kind of documentation, if there's such.
Typically the point is _not_ to care about them. You use auto, so you don't care
what the type actually is. If you want to pass them to a function, you have it
be a templated function. Perhaps it has a template constraint to verify that the
range is a particular type of range (such as std.range.isForwardRange!()) rather
than a totally arbitrary type, but you're not supposed to have to care that map
returns a Map object. Heck, exactly what type of range it is depends on what
type of range the one you gave to map was (e.g. if you gave map a random access
range - such as an array - than map returns a version of Map which is random
access range, whereas if you fed it a range which isn't a random access range,
then it isn't a random access range). You're not supposed to have to care. So,
to some extent at least, the documentation tries to bury it (which is definitely
better than telling you all of its gory details which is more along the lines of
what it did in the past).
If you want to know what the return type of a function is, use typeof. And if
you _really_ want to know what that return type actually looks like, then you
need to look at the source code (which would be in
dmd2/src/phobos/std/algorithm.d in the after you unzip the dmd zip file). But
you're just not supposed to have to care. I'm sure that the documentation could
be improved, but it is better than it used to be, and auto removes most of the
need to worry about what the exact type a return value is.
Also I wish to point out that the layout and presentation of some of
phobos ddoc pages are, IMHO and as I said before, a little bit of a
mess. Wish they could look more like javadoc, or at least more organized.
It's better than it used to be. I'm sure that it will improve more in the
future. But there are higher priorities (like bug fixing), so it's not something
that's likely to happen right away - certainly not massive change. I don't
expect that it will ever look quite like javadoc does, but it should be getting
better eventually. In theory, ddoc output can be made to look like pretty much
anything (javadoc included) - and what's up on the site is definitely better
than
what you get by default - but that means that someone has to do the work to make
it look like whatever looks really good (which is one of those things which is
highly subjective). It's improving, but slowly.
- Jonathan M Davis
I'm not criticizing ddoc color or fonts. I mean, for example, in the
index of symbols at the beginning of every ddoc page, there are
functions, constants, classes, and templates, all mixed and each next to
the other. It doesn't even have an alphabetic ordering. It was difficult
to me at first sight to understand where to look for things. Maybe it's
not that important as bugfixes, but when new programmers get close to D2
(even old D1 fans, like myself), I'm afraid that more than one could
feel some frustration.
Tom;
