dcollections ArrayList pb with mixin template
Hi, I have a problem with a mixin template. More exact with an
Arraylist!T within a mixin template.
Given.
void main() {
auto p = new Person(Hans, 32);
p ~= new Person(Steve, 40);
p ~= new Person(Bjoern, 101);
}
class Person {
private string _name;
private uint _age;
mixin TLinkList;
this(string name, uint age) {
this._name = name;
this._age = age;
}
}
mixin template TLinkList() {
alias typeof(this) T;
alias ArrayList!T TList;
T[] pa;
auto pl = new TList(pa); // This does not work !
void opCatAssign(T v) {
pa ~= v;
}
}
Error: non-constant expression new ArrayList(pa)main.d
Ideas ?
Thanks Bjoern
Re: dcollections ArrayList pb with mixin template
On Thu, 01 Jul 2010 15:36:53 -0400, BLS windev...@hotmail.de wrote:
Hi, I have a problem with a mixin template. More exact with an
Arraylist!T within a mixin template.
Given.
void main() {
auto p = new Person(Hans, 32);
p ~= new Person(Steve, 40);
p ~= new Person(Bjoern, 101);
}
class Person {
private string _name;
private uint _age;
mixin TLinkList;
this(string name, uint age) {
this._name = name;
this._age = age;
}
}
mixin template TLinkList() {
alias typeof(this) T;
alias ArrayList!T TList;
T[] pa;
auto pl = new TList(pa); // This does not work !
void opCatAssign(T v) {
pa ~= v;
}
}
Error: non-constant expression new ArrayList(pa)main.d
Ideas ?
Thanks Bjoern
I'm thinking it has to do with you trying to create a member with that
line.
I think a member initializer has to be a constant expression, like int i =
1. Anything else has to be done in the constructor. This kinda sucks,
because you can't initialize members with their defaults where you declare
them, but it's the way D works.
-Steve
Re: dcollections ArrayList pb with mixin template
On 01/07/2010 22:59, Steven Schveighoffer wrote:
On Thu, 01 Jul 2010 15:36:53 -0400, BLS windev...@hotmail.de wrote:
Hi, I have a problem with a mixin template. More exact with an
Arraylist!T within a mixin template.
Given.
void main() {
auto p = new Person(Hans, 32);
p ~= new Person(Steve, 40);
p ~= new Person(Bjoern, 101);
}
class Person {
private string _name;
private uint _age;
mixin TLinkList;
this(string name, uint age) {
this._name = name;
this._age = age;
}
}
mixin template TLinkList() {
alias typeof(this) T;
alias ArrayList!T TList;
T[] pa;
auto pl = new TList(pa); // This does not work !
void opCatAssign(T v) {
pa ~= v;
}
}
Error: non-constant expression new ArrayList(pa) main.d
Ideas ?
Thanks Bjoern
I'm thinking it has to do with you trying to create a member with that
line.
I think a member initializer has to be a constant expression, like int i
= 1. Anything else has to be done in the constructor. This kinda sucks,
because you can't initialize members with their defaults where you
declare them, but it's the way D works.
-Steve
Thanks for the feedback Steve.
IMHO it should work.. One reason is that C.E. Miller has created a
Circularly-linked list module, containing a portable linked list
template mixin. Indeed Christophers implementation is different in that
the LinkList is part of the mixin template...
http://www.dprogramming.com/list.php
2) Commenting the auto pl = new TList() line out makes the snippet work.
mixin template TLinkList() {
alias typeof(this) T;
alias ArrayList!T TList;
T[] pa;
//auto pl = new TList(pa); // NOW IT WORKS !
void opCatAssign(T v) {
pa ~= v;
}
Well I am a D noob. Have to investigate a bit more, and of course any
help is welcome :)
Bjoern
Re: dcollections ArrayList pb with mixin template
Steven Schveighoffer: I think a member initializer has to be a constant expression, like int i = 1. Anything else has to be done in the constructor. There are the static constructors too, for modules, structs, classes. Bye, bearophile
Re: dcollections ArrayList pb with mixin template
On 02/07/2010 00:26, bearophile wrote: Steven Schveighoffer: I think a member initializer has to be a constant expression, like int i = 1. Anything else has to be done in the constructor. There are the static constructors too, for modules, structs, classes. Bye, bearophile Hi bearophile, I don't understand (in this context) . Can you please elaborate a bit more ? thanks bjoern
Re: Mixing operations with signed and unsigned types
Stewart Gordon: That code needs to be fixed? My point was that being forced to use signed types for values that cannot possibly be negative doesn't to me constitute fixing anything. Yes, in my opinion it needs to be fixed. Using unsigned integers in D is a hazard, so if you use them where they are not necessary (and representing positive-only values is often not one of such cases) then you are doing something wrong, or doing premature optimization. Using a unsigned value to represent a positive-only value is not going to increase your program safety as it happens for example in Delphi, in D it decreases your program resilience. Using size_t and uint in your code where you can use an int is something that needs to be fixed, in my opinion. Normal D programmers writing very mundane code must not be forced to face unsigned values every few lines of code. Unsigned values in D are quite bug-prone, so the language has to avoid putting them on your plate every time you want to write some code. You need to be free to use them when you want, but it's better for you to use them only when necessary. Unsigned values have some purposes, like representing bit fields, representing very large integers (over signed values range) when you are optimizing your code and with your profiler you have found a hot spot and you want to reduce space used or increase performance, to work with bitwise operators, to work with bit fields, and few more. But letting all programmers, even D newbies mess with unsigned values every time they want to use an array length is something that will cause a very large number of bugs and wasted programming time in future D programs. You will need a hard evidence to convince me this is false. If you want to make your D code a bit more safe you have to write code like: cast(int)somearray_.length - degree because if you write more normal expressions like: somearray_.length - degree You can quickly put some bugs in your code :-) I have written something like 300_000 lines of D code so far, and I have found a good number of unsigned-derived bugs in my code. Good luck with your code. And by the way, in C# you have ways to use unsigned values, but I think array lengths and indexes are signed. Maybe they know better than Walter and you about this design detail. Bye, bearophile
Re: dcollections ArrayList pb with mixin template
BLS:
I don't understand (in this context) . Can you please elaborate a bit more ?
I have not shown you code because I don't understand your context. But you can
put inside static this() {...} code that can't be run statically, like the
initialization of a run-time thing.
Bye,
bearophile
