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digitalmars.D - array concatenation issue? or me being stupid

reply Tobias Kieslich <tobias justdreams.de> writes:
Hi,

dmd version was 2.012 for this.

	I'm sorry if that should have gone to learn-d but it also might be a
bug. Anyway, I'm here to to get some insight.
Coming from scripting languages (Python, JavaScript as fnctional
language, etc) I try to come to terms with the rules of a language like
D.
I tried some array concatenation the other day to figure out about when
I can use a~=1 vs a~=[1]. Where the first strongly resambles constructs
like a.append(1) and the latter a += [1] in python. Anyway, approaching
multidimensional arrays I ran into an obvious issue, that I have to
write:

	int [][] a =[[0,1],[2,3]];
	a ~= [4,5];    //fail
	a ~= [[4,5]];  //success

because D inspects the first element of an array to determine it's type.
Now, here it is where it gets weird. Dynamic arrays of static arrays:

	int [2][] b =[[0,1],[2,3]];
	b ~= [[4,5]];  // fail, because concatenate [2u][] with [][1u]
	b ~= [4,5];    // success but wrong result as b holds now:
	// [[0 1] [2 3] [4 5] [0 0]]

How do I concatenate that properly?

Thanks,
	Tobias

some readyly compilable sample code:

import std.stdio;

int main() {
	writefln("multi dim arrays -- dynamic");
	/// multi dimensional arrays
	int [][] a = [[1,2],[3,4]];
	writefln("%s --- length: %d", a, a.length);
	//a = a ~ [9,10];
	a = a ~ [[9,10]]; // success, can concatenate 2 arrays of same type and
structure
	writefln("%s --- length: %d", a, a.length );
	// success, D knows only that it's an array of arrays, not about the length of
the arrays
	// because we initialized as dynamic arrays
	a = a ~ [[11,12,13]];
	writefln("%s --- length: %d", a, a.length );


	writefln("\nmulti dim arrays -- dynamic of static");
	int [2][] y = [[1,2],[3,4]];
	writefln("%s --- length: %d", y, y.length );
	//y = y ~ [[9,10]]; // fail because concatenate [2u][] with [][1u]
	y = y ~ [9,10]; // success, but wrong result
	writefln("%s --- length: %d", y, y.length );
	// fail, because we initialized as arrays of static length of 2
	//y = y ~ [11,12,13];

	return 1;
}
Mar 18 2008
parent reply downs <default_357-line yahoo.de> writes:
Tobias Kieslich wrote:

 Hi,
 
 dmd version was 2.012 for this.
 
 	I'm sorry if that should have gone to learn-d but it also might be a
 bug. Anyway, I'm here to to get some insight.
 Coming from scripting languages (Python, JavaScript as fnctional
 language, etc) I try to come to terms with the rules of a language like
 D.
 I tried some array concatenation the other day to figure out about when
 I can use a~=1 vs a~=[1]. Where the first strongly resambles constructs
 like a.append(1) and the latter a += [1] in python. Anyway, approaching
 multidimensional arrays I ran into an obvious issue, that I have to
 write:
 
 	int [][] a =[[0,1],[2,3]];
 	a ~= [4,5];    //fail
 	a ~= [[4,5]];  //success
 
 because D inspects the first element of an array to determine it's type.
 Now, here it is where it gets weird. Dynamic arrays of static arrays:
 
 	int [2][] b =[[0,1],[2,3]];
 	b ~= [[4,5]];  // fail, because concatenate [2u][] with [][1u]
 	b ~= [4,5];    // success but wrong result as b holds now:
 	// [[0 1] [2 3] [4 5] [0 0]]
 


Strange.
Using GDC 0.24/1.028 on 4.1.2, I get this:

gentoo-pc ~ $ cat test6.d; gdc test6.d -o test6 && ./test6
import std.stdio;

void main() {
        int[2][] b = [[0,1], [2,3]];
        b ~= [[4, 5]];
        b ~= [6, 7];
        writefln(b);
}
[[0,1],[2,3],[4,5],[6,7]]

So it's probably something that broke on the change to 2.0.

Could somebody please try to reproduce on DMD/1.0?

 --downs
Mar 18 2008
parent reply bearophile <bearophileHUGS lycos.com> writes:
downs:

 Using GDC 0.24/1.028 on 4.1.2, I get this:
 [[0,1],[2,3],[4,5],[6,7]]
 So it's probably something that broke on the change to 2.0.


It gives the same correct result on DMD 1.028.

Bye,
bearophile
Mar 18 2008
parent Tobias Kieslich <tobias justdreams.de> writes:
On Tue, 18 Mar 2008, bearophile wrote:


 downs:

 Using GDC 0.24/1.028 on 4.1.2, I get this:
 [[0,1],[2,3],[4,5],[6,7]]
 So it's probably something that broke on the change to 2.0.


 
 It gives the same correct result on DMD 1.028.


confiremd, 1.028 gives me the same okay result

Bye,
	Tobias
Mar 18 2008