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digitalmars.D.learn - Why doesn't this have a length?

reply Magnus Lie Hetland <magnus hetland.org> writes:
In a template class (with State and Input as template parameters), I 
have the following (private) member:

State[][Tuple!(const(State), const(Input))] transitions;

It works well enough, but for some reason I can't access its length 
attribute...? (If I define other simpler, similar private attributes, 
such as uint[uint], I can access their length in the same location 
where transition.length fails.)

I get an error message that seems to indicate that DMD is looking for a 
global identifier. I've tried instantiating with different types, e.g., 
uint.

Am I doing something illegal?-)

-- 
Magnus Lie Hetland
http://hetland.org
Mar 12 2012
parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Magnus Lie Hetland:


 Am I doing something illegal?-)


It looks legal. As usual I suggest to minimize the code, and show
us the reduced case that shows the problem :-)

Bye,
bearophile
Mar 12 2012
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 03/12/2012 08:59 AM, bearophile wrote:

 Magnus Lie Hetland:


 Am I doing something illegal?-)


 It looks legal. As usual I suggest to minimize the code, and show
 us the reduced case that shows the problem :-)

 Bye,
 bearophile


Let's please also see the exact error message. "an error message that 
seems to indicate that DMD is looking for a global identifier" is not 
clear to mortals like myself. :)

Ali
Mar 12 2012
parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 3/12/12, Ali =C7ehreli <acehreli yahoo.com> wrote:

 Let's please also see the exact error message. "an error message that
 seems to indicate that DMD is looking for a global identifier" is not
 clear to mortals like myself. :)


He probably means something like this:

struct State { }
struct Input { }
State[][Tuple!(const(State), const(Input))] transitions;

void main() {
    writeln(transitions.length);
}

test.d(20): Error: undefined identifier module test.length

Note that typeid doesn't work either:
writeln(typeid(transitions));
D:\DMD\dmd2\windows\bin\..\..\src\druntime\import\object.di(507):
Error: can only initialize const member key inside constructor

This seems to be an issue related with const. Without const both calls work=
.
Mar 12 2012
parent reply =?utf-8?Q?Simen_Kj=C3=A6r=C3=A5s?= <simen.kjaras gmail.com> writes:
On Mon, 12 Mar 2012 19:20:07 +0100, Andrej Mitrovic  =

<andrej.mitrovich gmail.com> wrote:


 On 3/12/12, Ali =C3=87ehreli <acehreli yahoo.com> wrote:

 Let's please also see the exact error message. "an error message that=





 seems to indicate that DMD is looking for a global identifier" is not=





 clear to mortals like myself. :)


 He probably means something like this:

 struct State { }
 struct Input { }
 State[][Tuple!(const(State), const(Input))] transitions;

 void main() {
     writeln(transitions.length);
 }

 test.d(20): Error: undefined identifier module test.length

 Note that typeid doesn't work either:
 writeln(typeid(transitions));
 D:\DMD\dmd2\windows\bin\..\..\src\druntime\import\object.di(507):
 Error: can only initialize const member key inside constructor

 This seems to be an issue related with const. Without const both calls=


  =


 work.


Weird. You get a different error message from what I get.
My reduced code:

struct Bar {
	const int t;
}

void main( ) {
	int[Bar] a;
	int n =3D a.length;
}

Error message:

Assertion failure: 'impl' on line 4407 in file 'mtype.c'

abnormal program termination

http://d.puremagic.com/issues/show_bug.cgi?id=3D7695
Mar 12 2012
parent reply Magnus Lie Hetland <magnus hetland.org> writes:
On 2012-03-13 02:27:46 +0000, Simen Kjærås said:


 Weird.


Indeed. Would've thought const AA keys would be reasonable. (In Python 
they're *required*... :)


 You get a different error message from what I get.
 My reduced code:


[snip]

 http://d.puremagic.com/issues/show_bug.cgi?id=7695


I guess this issue then covers both (despite the different error 
messages)? I'll just leave this alone (i.e., not submit any additional 
tickets), then (and cast away the constness for now; seems to help).

-- 
Magnus Lie Hetland
http://hetland.org
Mar 13 2012
parent reply "H. S. Teoh" <hsteoh quickfur.ath.cx> writes:
On Tue, Mar 13, 2012 at 10:02:02AM +0100, Magnus Lie Hetland wrote:

 On 2012-03-13 02:27:46 +0000, Simen Kjærås said:
 

Weird.


 
 Indeed. Would've thought const AA keys would be reasonable. (In
 Python they're *required*... :)


[...]

I'm of the opinion that AA keys should be *implicitly* immutable. It
makes no sense to have mutable AA keys:

	int[] mykey = [1,2,3,4];
	string[int[]] aa;
	aa[mykey] = "abc";
	mykey[0] = 2;	// monkey business: mykey has changed but aa
			// doesn't know about it
	assert(([1,2,3,4] in aa) !is null); // this will fail

But requiring the user to constantly type overly-long type specs like
string[immutable int[]] just makes AA's annoying to use, especially if
unqualified key types are always illegal.


T

-- 
Your inconsistency is the only consistent thing about you! -- KD
Mar 13 2012
parent Magnus Lie Hetland <magnus hetland.org> writes:
On 2012-03-13 14:24:37 +0000, H. S. Teoh said:


 Indeed. Would've thought const AA keys would be reasonable. (In
 Python they're *required*... :)


 [...]
 
 I'm of the opinion that AA keys should be *implicitly* immutable.


Seconded, whole-heartedly.

-- 
Magnus Lie Hetland
http://hetland.org
Mar 13 2012