Structs should not contain pointers to internal data
Saurabh Das
saurabh.das at silverleafcaps.com
Sun Jun 2 21:53:43 PDT 2013
Hello Learn-D,
I'm new to D from a C/C++ background. One caveat of defining structs in D
that I came across was that structs should be bit-wise relocatable and
hence should not contain pointers to internal data members.
So that essentially means that code of the form (below) is disallowed.
struct S1
{
int x;
int* p = &x;
}
What I'm wondering is, are references also disallowed? As in:
struct S2
{
int x;
ref int p = x;
}
I ask this because in C++, I have a telemetry class which publishes the
value of any member variable over TCP. I was trying to achieve similar
functionality in D and am wondering how to go about designing it.
Ideally I'd like to have:
struct Telemetry(T) ...
struct UsefulStruct
{
int importantValue;
auto tel1 = Telemetry!int(importantValue);
}
Essentially I'm asking whether the above is a valid construct in D.
Thanks,
Saurabh
On Mon, Jun 3, 2013 at 4:42 AM,
<digitalmars-d-learn-request at puremagic.com>wrote:
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> Today's Topics:
>
> 1. What tool(s) do you use to build a large D project? (coredumper)
> 2. Re: What tool(s) do you use to build a large D project?
> (Adam D. Ruppe)
> 3. Re: UFCS for classes with opCall( ... ) (Timon Gehr)
> 4. Re: until strange behavior (Jonathan M Davis)
> 5. isMutable doesn't work with enum ? (Temtaime)
> 6. Re: isMutable doesn't work with enum ? (Jonathan M Davis)
> 7. Re: isMutable doesn't work with enum ? (bearophile)
> 8. Re: isMutable doesn't work with enum ? (Temtaime)
> 9. Re: isMutable doesn't work with enum ? (Temtaime)
> 10. Re: isMutable doesn't work with enum ? (Jonathan M Davis)
> 11. Re: isMutable doesn't work with enum ? (Jonathan M Davis)
> 12. Re: until strange behavior (Jack Applegame)
> 13. Re: until strange behavior (Jonathan M Davis)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 02 Jun 2013 21:20:38 +0200
> From: "coredumper" <me at example.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: What tool(s) do you use to build a large D project?
> Message-ID: <etvbsbhiaukbnlxgixcy at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> Hello!
>
> What tool(s) do you use to build a D project? I looked at cmaked
> (and cmaked2) but both projects seem not to be under active
> development, there is also a bunch of other tools like dsss but
> all of them are an abandonware. So, if you are seriously using D,
> how do you build you projects? What is the mainstream way?
>
>
> ------------------------------
>
> Message: 2
> Date: Sun, 02 Jun 2013 21:26:43 +0200
> From: "Adam D. Ruppe" <destructionator at gmail.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: What tool(s) do you use to build a large D project?
> Message-ID: <qaythxlwuijhavdjhqqi at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> I just use plain old makefiles. I generally start with
>
> all:
> dmd *.d <flags>
>
> and then break it out just like I would with a C++ project when
> the need arises (actually pretty rare, this works quite well even
> for my larger stuff).
>
>
> ------------------------------
>
> Message: 3
> Date: Sun, 02 Jun 2013 22:48:47 +0200
> From: Timon Gehr <timon.gehr at gmx.ch>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: UFCS for classes with opCall( ... )
> Message-ID: <kogb3f$ehk$1 at digitalmars.com>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> On 06/01/2013 02:22 PM, ParticlePeter wrote:
> > Hello,
> >
> > after watching Walters Talk about Component Programming ( link Bellow )
> > I was quite fond of his pipelining approach.
> > I tried the following and had to realize that this way using UFCS isn't
> > working ( or I do something wrong ).
> >
> > // I want to write On Canvas1 | draw Shape1 | draw Shape2 | ... in code
> > ( not working ):
> > canvas1.shape1.shape2.draw()
> >
> > // Which in essence would be ( working ):
> > shape2( shape1( canvas1 ) ).draw()
> > ...
>
> UFCS is working with opCall already.
>
> The reason your code does not work is that UFCS only works with
> module-level symbols (and with the latest release also for locally
> imported symbols IIRC.)
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Sun, 02 Jun 2013 13:50:15 -0700
> From: Jonathan M Davis <jmdavisProg at gmx.com>
> To: "digitalmars.D.learn" <digitalmars-d-learn at puremagic.com>
> Subject: Re: until strange behavior
> Message-ID: <2641846.fA8uGAeyYA at lyonel>
> Content-Type: text/plain; charset="utf-8"
>
> On Sunday, June 02, 2013 15:20:31 Temtaime wrote:
> > Why
> >
> > char arr[3] = "abc";
> > arr[].until('b').front has type of dchar ???
>
> http://stackoverflow.com/questions/12288465
>
> - Jonathan M Davis
>
>
> ------------------------------
>
> Message: 5
> Date: Mon, 03 Jun 2013 00:14:34 +0200
> From: "Temtaime" <temtaime at gmail.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: isMutable doesn't work with enum ?
> Message-ID: <eruaxrnxigbyqamlxemq at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> Hi!
>
> enum int a = 5;
> writeln(isMutable!(typeof(a)));
>
> Writes true. Why? How i can figure out if variable is "enum"
> constant ?
> Thanks.
> Regards.
>
>
> ------------------------------
>
> Message: 6
> Date: Sun, 02 Jun 2013 15:23:36 -0700
> From: Jonathan M Davis <jmdavisProg at gmx.com>
> To: "digitalmars.D.learn" <digitalmars-d-learn at puremagic.com>
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <4584128.RAFB2m748R at lyonel>
> Content-Type: text/plain; charset="utf-8"
>
> On Monday, June 03, 2013 00:14:34 Temtaime wrote:
> > Hi!
> >
> > enum int a = 5;
> > writeln(isMutable!(typeof(a)));
> >
> > Writes true. Why? How i can figure out if variable is "enum"
> > constant ?
> > Thanks.
> > Regards.
>
> isMutable just checks whether the type const or immutable, and is true if
> it's
> neither. And int is mutable. Also, what you've declared there is a manifest
> constant, not really an enum in the normal sense. It would have to have a
> type
> name for it be a full-on enum. Something more like
>
> enum E : int { a = 5 }
>
> Your a there is not typed as an enum at all. The difference between it and
> doing something like
>
> immutable int a = 5;
>
> is the fact a manifest constant does not have an address and gets
> copy-pasted
> where it's used, which is why doing something like
>
> enum arr = [1, 2, 3, 4, 5];
>
> is often considered a bad idea. An array gets allocated every time that the
> manifest constant is used, because using arr effectively just pastes [1,
> 2, 3,
> 4, 5] in its place.
>
> However, if you really want to check whether something is an enum or not,
> do
>
> is(E == enum)
>
> And with your original definition, is(typeof(a) == enum) will be false,
> because
> its type is int.
>
> - Jonathan M Davis
>
>
> ------------------------------
>
> Message: 7
> Date: Mon, 03 Jun 2013 00:30:42 +0200
> From: "bearophile" <bearophileHUGS at lycos.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <hpdebexqxrzebtgixoua at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> Temtaime:
>
> >
> > enum int a = 5;
> > writeln(isMutable!(typeof(a)));
> >
> > Writes true. Why?
>
> If you run this:
>
> enum int a = 5;
> pragma(msg, typeof(a));
> void main() {}
>
> It prints "int". An int is mutable.
>
>
> > How i can figure out if variable is "enum" constant ?
>
> Why do you need to know that?
>
> Bye,
> bearophile
>
>
> ------------------------------
>
> Message: 8
> Date: Mon, 03 Jun 2013 00:34:49 +0200
> From: "Temtaime" <temtaime at gmail.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <jfpkdgmmvfsifarokmsu at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> It's intresting.
> So the only way to pass "a" to overloaded function like that ?
>
> void foo(T)(ref T) { writeln("true"); }
> void foo(T)(auto ref in T) { writeln("false"); }
>
> enum int a = 10;
> foo(a); // false
>
> int b = 1;
> foo(b); // true
>
>
> ------------------------------
>
> Message: 9
> Date: Mon, 03 Jun 2013 00:36:46 +0200
> From: "Temtaime" <temtaime at gmail.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <ecwvfgfajylndwlyjccu at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> I'm writing serializer and it iterates all members of struct.
> It compares fields marked as "enum" when reading from file to
> check BOM, for example.
>
> I'm using enum now because const members are deprecated in 2.063.
>
>
> ------------------------------
>
> Message: 10
> Date: Sun, 02 Jun 2013 15:40:32 -0700
> From: Jonathan M Davis <jmdavisProg at gmx.com>
> To: "digitalmars.D.learn" <digitalmars-d-learn at puremagic.com>
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <1713172.WrMD0SRKMg at lyonel>
> Content-Type: text/plain; charset="utf-8"
>
> On Monday, June 03, 2013 00:34:49 Temtaime wrote:
> > It's intresting.
> > So the only way to pass "a" to overloaded function like that ?
> >
> > void foo(T)(ref T) { writeln("true"); }
> > void foo(T)(auto ref in T) { writeln("false"); }
> >
> > enum int a = 10;
> > foo(a); // false
> >
> > int b = 1;
> > foo(b); // true
>
> ref only accepts lvalues. An enum is not an lvalue. auto ref makes it so
> that
> if the templated function is passed an lvalue, it generates a ref version,
> whereas if it's passed an rvalue, it generates a non-ref version. It would
> appear that the compiler considers ref to be a better match than auto ref
> (as
> opposed to giving an error), so when you pass foo an lvalue, the ref
> version
> gets called, but when you pass it an rvalue, the only viable overload is
> the
> auto ref one, so it gets called.
>
> - Jonathan M Davis
>
>
> ------------------------------
>
> Message: 11
> Date: Sun, 02 Jun 2013 15:42:09 -0700
> From: Jonathan M Davis <jmdavisProg at gmx.com>
> To: "digitalmars.D.learn" <digitalmars-d-learn at puremagic.com>
> Subject: Re: isMutable doesn't work with enum ?
> Message-ID: <19062665.b9QIKb6H1G at lyonel>
> Content-Type: text/plain; charset="utf-8"
>
> On Monday, June 03, 2013 00:36:46 Temtaime wrote:
> > I'm writing serializer and it iterates all members of struct.
> > It compares fields marked as "enum" when reading from file to
> > check BOM, for example.
> >
> > I'm using enum now because const members are deprecated in 2.063.
>
> The equivalent to what const members were doing before is static const.
> static
> was being implicitly tacked onto the const. enums do something subtley
> different. static const variables are actually variables with addresses
> (lvalues), whereas enums have no address and are rvalues.
>
> - Jonathan M Davis
>
>
> ------------------------------
>
> Message: 12
> Date: Mon, 03 Jun 2013 01:04:28 +0200
> From: "Jack Applegame" <japplegame at gmail.com>
> To: digitalmars-d-learn at puremagic.com
> Subject: Re: until strange behavior
> Message-ID: <qahcvglusxgrkshoocti at forum.dlang.org>
> Content-Type: text/plain; charset=utf-8; format=flowed; delsp=no
>
> On Sunday, 2 June 2013 at 20:50:31 UTC, Jonathan M Davis wrote:
>
> > http://stackoverflow.com/questions/12288465
>
> Lets have string of chars, and it contains UTF-8 string.
> Does front(str[]) automatically convert first unicode character
> to UTF-32 and returns it?
> I made a test case and answer is: "Yes, it does!"
> May be this make sense. But such implicit conversion confuses
> everyone whom I asked.
> Therefore, string is not ordinary array (in Phobos context), but
> special array with special processing rules.
>
> I'm moving from C++ and often ask myself: "why D has so much
> hidden confusing things?"
>
>
> ------------------------------
>
> Message: 13
> Date: Sun, 02 Jun 2013 16:12:09 -0700
> From: Jonathan M Davis <jmdavisProg at gmx.com>
> To: "digitalmars.D.learn" <digitalmars-d-learn at puremagic.com>
> Subject: Re: until strange behavior
> Message-ID: <10181668.aRRsJoJz5o at lyonel>
> Content-Type: text/plain; charset="utf-8"
>
> On Monday, June 03, 2013 01:04:28 Jack Applegame wrote:
> > On Sunday, 2 June 2013 at 20:50:31 UTC, Jonathan M Davis wrote:
> > > http://stackoverflow.com/questions/12288465
> >
> > Lets have string of chars, and it contains UTF-8 string.
> > Does front(str[]) automatically convert first unicode character
> > to UTF-32 and returns it?
> > I made a test case and answer is: "Yes, it does!"
> > May be this make sense. But such implicit conversion confuses
> > everyone whom I asked.
> > Therefore, string is not ordinary array (in Phobos context), but
> > special array with special processing rules.
> >
> > I'm moving from C++ and often ask myself: "why D has so much
> > hidden confusing things?"
>
> The language treats strings as arrays of code units. The standard library
> treats them as ranges of code points. Yes, this can be confusing, but we
> need
> both. In order to operate on strings efficiently, they need to be made up
> of
> code units, but correctness requires code points. This means that the
> complexity is to a great extent an intrinsic part of dealing with strings
> properly. In C++, people usually just screw it up and treat char as if it
> were
> a character when in fact it's not. It's a piece of one.
>
> Whether we went about handling the complexity of code units vs code points
> in
> the best manner is debatable, but it can't be made simple if you want both
> efficiency and correctness. A better approach might have been to have a
> string
> type which operated on code points and held the code units internally so
> that
> everything operated on code points by default, but the library stuff was
> added
> later, and Walter Bright tends to think that everyone should understand
> Unicode well, so the decisions he makes with regards to that aren't always
> the
> best (since most people don't understand Unicode well and don't want to
> care).
>
> What we have actually works quite well, but it does require that you come
> to
> at least a basic understanding of the difference between code units and
> code
> points.
>
> - Jonathan M Davis
>
>
> ------------------------------
>
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> End of Digitalmars-d-learn Digest, Vol 89, Issue 5
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