digitalmars.D.learn - Some quick questions
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (48/48) Aug 07 2007 Hi, I have some quick questions:
- Chris Nicholson-Sauls (14/66) Aug 07 2007 I remember there being a reason... darned if I recall it exactly,
- BCS (22/42) Aug 07 2007 every time I see the index changed my toes curl. It just seems wrong.
- Regan Heath (5/51) Aug 08 2007 I'd use a for loop. That said it would be nice if there was a nicer way...
- Jarrett Billingsley (9/12) Aug 08 2007 Of course, depending on the container, changing the index may or may not...
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (11/11) Aug 08 2007 Thanks for all your replies. I have one more quick question: how do I
- BCS (30/43) Aug 08 2007 ;struct S {
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (17/22) Aug 08 2007 How dumb of me :-| sorry.
- Carlos Santander (6/36) Aug 08 2007 This is normal D behavior due to its look-up rules. I'm sure someone els...
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (13/15) Aug 09 2007 Didn't know that, thanks.
- Carlos Santander (6/21) Aug 09 2007 Good question. It has been in the issue database for a while now
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (10/10) Aug 22 2007 Hi,
- Jarrett Billingsley (22/32) Aug 22 2007 Because those expressions aren't constant. Hate to sound obvious XD
- =?UTF-8?B?TcOhcmNpbyBGYXVzdGlubw==?= (2/11) Aug 22 2007 Thanks! ;-)
Hi, I have some quick questions:
(1.) Why does version 2.0 of the compiler doesn't allow changing the
index of a foreach loop? For example:
;string format = "%s";
;
;foreach (i, c; format) {
; if (c != '%') {
; // ...
; continue;
; }
;
; switch (format[++i]) {
; case 's':
; // ...
; break;
; // ...
; }
;}
Instead of the (more tedious):
;string format = "%s";
;bool was_escape = false;
;
;foreach (i, c; format) {
; if (was_escape) {
; was_escape = false;
; continue;
; }
; if (c != '%') {
; // ...
; continue;
; }
;
; was_escape = true;
; switch (format[++i]) {
; case 's':
; // ...
; break;
; // ...
; }
;}
(2.) What's the rationale for opEquals returning an int, given that we
have a bool data type? (And it clearly returns a boolean value.)
(3.) Shouldn't the toHash method of the Object class return
"cast(hash_t) cast(void*) this" instead of "cast(uint) cast(void*)
this", since the hash_t type is defined differently for x86 and x64?
(4.) Shouldn't the equals method of the TypeInfo_i class use casts to
int's instead of uint's, since that TypeInfo class is for int's?
Thanks!
Aug 07 2007
Chris Nicholson-Sauls <ibisbasenji gmail.com> Márcio Faustino wrote:Hi, I have some quick questions: (1.) Why does version 2.0 of the compiler doesn't allow changing the index of a foreach loop? For example: ;string format = "%s"; ; ;foreach (i, c; format) { ; if (c != '%') { ; // ... ; continue; ; } ; ; switch (format[++i]) { ; case 's': ; // ... ; break; ; // ... ; } ;} Instead of the (more tedious): ;string format = "%s"; ;bool was_escape = false; ; ;foreach (i, c; format) { ; if (was_escape) { ; was_escape = false; ; continue; ; } ; if (c != '%') { ; // ... ; continue; ; } ; ; was_escape = true; ; switch (format[++i]) { ; case 's': ; // ... ; break; ; // ... ; } ;}I remember there being a reason... darned if I recall it exactly, though. And actually I think the reasoning had mainly to do with inout indices, as changing them potentially leads to undefined behavior. (Just like modifying an array while foreach'ing over it is a problem.) Times like this I wish there was a 'skip' command for loops, or at least some reasonable allowances.(2.) What's the rationale for opEquals returning an int, given that we have a bool data type? (And it clearly returns a boolean value.)Historical reasons. Although, you actually /can/ define it as returning bool and nothing will break -- D's bool and int types are the same under the hood, and implicitly cast.(3.) Shouldn't the toHash method of the Object class return "cast(hash_t) cast(void*) this" instead of "cast(uint) cast(void*) this", since the hash_t type is defined differently for x86 and x64?Yes. Yes it should. :)(4.) Shouldn't the equals method of the TypeInfo_i class use casts to int's instead of uint's, since that TypeInfo class is for int's?Possibly. Unless there's some tiny gain in casting to an unsigned type over a signed? (I really doubt it.) -- Chris Nicholson-Sauls
Aug 07 2007
Reply to Márcio,
Hi, I have some quick questions:
(1.) Why does version 2.0 of the compiler doesn't allow changing the
index of a foreach loop? For example:
;string format = "%s";
;
;foreach (i, c; format) {
; if (c != '%') {
; // ...
; continue;
; }
;
; switch (format[++i]) {
; case 's':
; // ...
; break;
; // ...
; }
;}
every time I see the index changed my toes curl. It just seems wrong.
I'd do this:
;string format = "%s";
;int next = 0;
;foreach (i, c; format)
;{
; if(i != next) continue;
; if (c != '%')
; {
; // ...
; continue;
; }
; next = i + 1;
; switch (format[next])
; {
; case 's':
; // ...
; break;
; // ...
; }
;}
Aug 07 2007
BCS wrote:Reply to Márcio,I'd use a for loop. That said it would be nice if there was a nicer way to do this with foreach as it's the only 'container agnostic' way of iterating, right? ReganHi, I have some quick questions: (1.) Why does version 2.0 of the compiler doesn't allow changing the index of a foreach loop? For example: ;string format = "%s"; ; ;foreach (i, c; format) { ; if (c != '%') { ; // ... ; continue; ; } ; ; switch (format[++i]) { ; case 's': ; // ... ; break; ; // ... ; } ;}every time I see the index changed my toes curl. It just seems wrong. I'd do this: ;string format = "%s"; ;int next = 0; ;foreach (i, c; format) ;{ ; if(i != next) continue; ; if (c != '%') ; { ; // ... ; continue; ; } ; next = i + 1; ; switch (format[next]) ; { ; case 's': ; // ... ; break; ; // ... ; } ;}
Aug 08 2007
"Regan Heath" <regan netmail.co.nz> wrote in message news:f9btus$2oqv$1 digitalmars.com...I'd use a for loop. That said it would be nice if there was a nicer way to do this with foreach as it's the only 'container agnostic' way of iterating, right?Of course, depending on the container, changing the index may or may not make any sense. Arrays are linear, maps are not. So if you have a foreach loop that could skip elements, it would only be useful on those containers where skipping ahead made sense (you lose one element of that agnosticity (if that's even a word (which I doubt it is :X ))). I'd say when you start needing to change the index, use a for loop; that's what it's there for.
Aug 08 2007
Thanks for all your replies. I have one more quick question: how do I
access union's members, inside a struct? For example:
;struct S {
; union u {
; ubyte b;
; uint i;
; }
;}
;S s;
;ubyte b = s.u.b; // Error: need 'this' to access member b
Thanks!
Aug 08 2007
Reply to Márcio,
Thanks for all your replies. I have one more quick question: how do I
access union's members, inside a struct? For example:
;struct S {
; union u {
; ubyte b;
; uint i;
; }
;}
;S s;
;ubyte b = s.u.b; // Error: need 'this' to access member b
Thanks!
;struct S {
; union u {
; ubyte b;
; uint i;
; }
;}
;S s;
;ubyte b = s.u.b; // Error: need 'this' to access member b
The reason that doesn’t work is that the uses of union there is a type
deceleration,
not a member declaration. So you get a struct without any content.
option 1 use anonymous unions
;struct S {
; union {
; ubyte b;
; uint i;
; }
;}
;S s;
;ubyte b = s.b;
option 2:
;struct S {
; union U {
; ubyte b;
; uint i;
; }
; U u;
;}
;S s;
;ubyte b = s.u.b;
Aug 08 2007
BCS wrote:The reason that doesn’t work is that the uses of union there is a type deceleration, not a member declaration. So you get a struct without any content. (...)How dumb of me :-| sorry. Here's another question, given these 2 files: // F1.d ------------------------- module F1; import F2; void f(int i, int j) {} void main() { f(1); } // F2.d ------------------------- module F2; void f(int i) {} Why does the compiler says: function F1.f (int,int) does not match parameter types (int) Error: expected 2 arguments, not 1 Looks like the import of F2 isn't working, because if I replace f(1) with F2.f(1), it works ok. Thanks!
Aug 08 2007
Márcio Faustino escribió:BCS wrote:alias F2.f f;The reason that doesn’t work is that the uses of union there is a type deceleration, not a member declaration. So you get a struct without any content. (...)How dumb of me :-| sorry. Here's another question, given these 2 files: // F1.d ------------------------- module F1; import F2;void f(int i, int j) {} void main() { f(1); } // F2.d ------------------------- module F2; void f(int i) {} Why does the compiler says: function F1.f (int,int) does not match parameter types (int) Error: expected 2 arguments, not 1 Looks like the import of F2 isn't working, because if I replace f(1) with F2.f(1), it works ok. Thanks!This is normal D behavior due to its look-up rules. I'm sure someone else will give you a more detailed explanation. -- Carlos Santander Bernal
Aug 08 2007
Carlos Santander wrote:This is normal D behavior due to its look-up rules. I'm sure someone else will give you a more detailed explanation.Didn't know that, thanks. Another question, why pointers to structs are automatically dereferenced when accessing members, but I cannot use them in "with" statements? For example: struct S { int i; char c; } S s; S* ps = &s; with (s) {} with (*ps) {} // Would also be nice if I could do: with (ps)
Aug 09 2007
Márcio Faustino escribió:
Another question, why pointers to structs are automatically dereferenced
when accessing members, but I cannot use them in "with" statements? For
example:
struct S {
int i;
char c;
}
S s;
S* ps = &s;
with (s) {}
with (*ps) {} // Would also be nice if I could do: with (ps)
Good question. It has been in the issue database for a while now
(http://d.puremagic.com/issues/show_bug.cgi?id=658), but Walter hasn't said
anything about it.
--
Carlos Santander Bernal
Aug 09 2007
Hi,
Does someone knows why isn't possible to do something like this:
//-------------------------------------------
import std.regexp;
class A {
RegExp pattern = new RegExp(".*");
}
RegExp[] patterns = [new RegExp(".*")];
//-------------------------------------------
Thanks,
Aug 22 2007
"Márcio Faustino" <m.faustino no.spam.gmail.com> wrote in message
news:fah26g$2ctr$1 digitalmars.com...
Hi,
Does someone knows why isn't possible to do something like this:
//-------------------------------------------
import std.regexp;
class A {
RegExp pattern = new RegExp(".*");
}
RegExp[] patterns = [new RegExp(".*")];
//-------------------------------------------
Thanks,
Because those expressions aren't constant. Hate to sound obvious XD
You can't use non-constant expressions (like function calls (well....
because of CTFE sometimes those are legal), 'new') as the initializer to
globals or class members because the compiler builds up their initializers
in the static data segment. Fortunately there are ways to do this:
class A
{
RegExp pattern;
this()
{
// Initialize dynamic members in the constructor.
pattern = new RegExp(".*");
}
}
RegExp[] patterns;
static this()
{
// Initialize dynamic globals in a static constructor.
patterns = [new RegExp(".*")];
}
Aug 22 2007
Jarrett Billingsley wrote:Because those expressions aren't constant. Hate to sound obvious XD You can't use non-constant expressions (like function calls (well.... because of CTFE sometimes those are legal), 'new') as the initializer to globals or class members because the compiler builds up their initializers in the static data segment. Fortunately there are ways to do this: (...)Thanks! ;-)
Aug 22 2007