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!

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

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;
;	// ...
;	}
;}

BCS wrote:
> 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;
> ;    // ...
> ;    }
> ;}

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?

Regan

"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.

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!

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;

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!

Márcio Faustino escribió:
> 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;
> 

alias F2.f f;

> 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

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)