object initialisers
IIRC objects are in the future. However, I'm currently writing C++ and
keep finding something annoying that I'd like to be able to do easily.
I have objects with attributes, such as
class Foo {
...
std::size_t spare;
std::size_t allocate;
std::size_t min_readline;
and then I have lots of constructors
public:
Foo (...) ... spare(0), allocate (4096), min_readline(80) ...
Foo (..., ...) ... spare(0), allocate (4096), min_readline(80) ...
Foo (..., ..., ...) ... spare(0), allocate (4096), min_readline(80) ...
As far as I can tell the only way to say spare should default to 0 is
to spell it out in each and every constructor. I'd like to write
class Foo {
...
std::size_t spare = 0
std::size_t allocate = 4096
std::size_t min_readline = 80
and have the compiler know that if I specify a member initialiser in my
my constructor, then that should be used, otherwise to default to using
the value I say. (To avoid the inevitable search/replace if I want to
change that value)
I can't figure out if there is a way to do this in C++ (the above syntax
isn't legal) and I'd like perl6 objects to make this sort of thing easy.
Nicholas Clark
Re: object initialisers
Nicholas Clark wrote:
class Foo {
...
std::size_t spare = 0
std::size_t allocate = 4096
std::size_t min_readline = 80
and have the compiler know that if I specify a member initialiser in my
my constructor, then that should be used, otherwise to default to using
the value I say. (To avoid the inevitable search/replace if I want to
change that value)
That's actually valid Java syntax (modulo a trailing C;). The default
value can be any expression (as long as it doesn't involve a reference
to the object being constructed, IIRC).
In fact Java provides a notion of instance initialiser, run before
any specific constructor you're invoking, that initialises such fields,
and may run other code.
The details aren't very clear to me, since I haven't written any Java
code since almost two years. I'm sure someone will correct me if I'm
wrong /-/.
an idle question: returning from a nested call
So, as I sweat here in the salt mines of C++, longing for the
cleansing joy that Perl(5 or 6, I'd even take 4) is, I find myself
with the following problem:
Frequently, I find myself writing stuff like this:
void Ficp400::SaveRow(long p_row)
{
// if p_row is marked as deleted, return
if (GetStatus(row) FLX_ROW_DELETE) { return; }
...
}
As a general rule, I don't like comments. When I see a comment, I
want to turn it into a function name. So, I keep wanting to be able
to write the above code like so:
void Ficp400::SaveRow(long p_row)
{
Return_If_Is_Deleted(p_row);
...
}
Now, in C++ (or P6, FTM), I could make this work via a macro, but
that's ugly. In P6, I could make it work by passing the current
continuation down to Return_If_Is_Deleted and call the continuation if
the row is in fact deleted, but that will require an extra param. Is
there a way to make it work as written? I'm thinking maybe the
Ccaller object would have something that would allow me to jump to
the right point (i.e., caller[2]).
Just an idle thought,
--Dks
Re: an idle question: returning from a nested call
--- David Storrs [EMAIL PROTECTED] wrote:
So, as I sweat here in the salt mines of C++, longing for the
cleansing joy that Perl(5 or 6, I'd even take 4) is, I find myself
with the following problem:
Frequently, I find myself writing stuff like this:
void Ficp400::SaveRow(long p_row)
{
// if p_row is marked as deleted, return
if (GetStatus(row) FLX_ROW_DELETE) { return; }
...
}
As a general rule, I don't like comments. When I see a comment, I
want to turn it into a function name. So, I keep wanting to be able
to write the above code like so:
void Ficp400::SaveRow(long p_row)
{
Return_If_Is_Deleted(p_row);
...
}
sub Ficp400::SaveRow(Int $p_row)
{
return if IsDeleted($p_row);
}
Re: an idle question: returning from a nested call
--- Austin Hastings [EMAIL PROTECTED] wrote:
--- David Storrs [EMAIL PROTECTED] wrote:
So, as I sweat here in the salt mines of C++, longing for the
cleansing joy that Perl(5 or 6, I'd even take 4) is, I find myself
with the following problem:
Frequently, I find myself writing stuff like this:
void Ficp400::SaveRow(long p_row)
{
// if p_row is marked as deleted, return
if (GetStatus(row) FLX_ROW_DELETE) { return; }
...
}
As a general rule, I don't like comments. When I see a comment, I
want to turn it into a function name. So, I keep wanting to be
able
to write the above code like so:
void Ficp400::SaveRow(long p_row)
{
Return_If_Is_Deleted(p_row);
...
}
sub Ficp400::SaveRow(Int $p_row)
{
return if IsDeleted($p_row);
}
But if you really need to make a function out of it, see the Cleave
keyword.
=Austin
Re: an idle question: returning from a nested call
On Thu, Jun 12, 2003 at 03:12:32PM -0700, Austin Hastings wrote:
sub Ficp400::SaveRow(Int $p_row)
{
return if IsDeleted($p_row);
}
*laugh* Well, yes, there is always the obvious way. I had wanted
something that would be reusable between multiple function, though
(sorry, should have said that explicitly).
I guess I got too caught up in the specific example; what I was really
curious about is if there was a way to skip up the stack on return.
And the answer, I see, is yes. Thanks for pointing me at Cleave.
Yeesh. Looks like I need to go back and reread A6 for a third time.
I obviously didn't understand it well enough.
--Dks
