Re: A use case for fromStringz

[spir]

On 04/16/2011 06:55 AM, Andrej Mitrovic wrote:

I wonder.. in all these years.. have they ever thought about using a
convention in C where the length is embedded as a 32/64bit value at
the pointed location of a pointer, followed by the array contents?


Sometimes called Pascal strings (actually, IIRC, the length is at the address 
/before/ the one pointed by the pointer). One of the important diffs between C 
 Pascal from the practical pov.

Actually, it's the same diff as C arrays vs true arrays like D's.

Denis
--
_
vita es estrany
spir.wikidot.com

Vector operations doesn't convert to a common type?

[simendsjo]

int[3]   a = [1,2,4];
float[3] b = [1,2,4];
float[3] c;
// Why doesn't this work?
c = a[] + b[]; // Error: incompatible types for ((a[]) + (b[])): 
'int[]' and 'float[]'

// When this works?
c[0] = a[0] + b[0];
c[1] = a[1] + b[1];
c[2] = a[2] + b[2];
assert(c == [2,4,8]);

Re: Vector operations doesn't convert to a common type?

[simendsjo]

On 16.04.2011 12:12, simendsjo wrote:

int[3] a = [1,2,4];
float[3] b = [1,2,4];
float[3] c;
// Why doesn't this work?
c = a[] + b[]; // Error: incompatible types for ((a[]) + (b[])): 'int[]'
and 'float[]'
// When this works?
c[0] = a[0] + b[0];
c[1] = a[1] + b[1];
c[2] = a[2] + b[2];
assert(c == [2,4,8]);


I tried using a template mixin to avoid having to type this all over, 
but I cannot get it to work.. I think I have something wrong with my 
alias usage, but that's just speculating :)


mixin template ArrayVectorOp(string op, alias dest, alias a, alias b, int I)
if(dest.length == a.length  dest.length == b.length  I = 1  I = 
dest.length) {

// dest[I-1] = a[I-1] op b[I-1]
mixin(dest.stringof~[~(I-1).stringof~]
   = 
  ~a.stringof~[~(I-1).stringof~]
  ~op
  ~b.stringof~[~(I-1).stringof~];);

static if(I  1)
mixin ArrayVectorOp!(op, dest, a, b, I-1);
}

void main() {
int[3]   a = [1,   2,   3];
float[3] b = [2.1, 3.2, 4.3];
float[3] c;
mixin ArrayVectorOp!(+, c, a, b, a.length);
assert(c == [3.1, 5.2, 7.3]);
}


Gives the following output:

t.d(4): no identifier for declarator c[3 - 1]
t.d(4): Error: c is used as a type
t.d(4): Error: cannot implicitly convert expression (cast(float)a[2u] + 
b[2u]) o

f type float to const(_error_[])
t.d(4): no identifier for declarator c[2 - 1]
t.d(4): Error: c is used as a type
t.d(4): Error: cannot implicitly convert expression (cast(float)a[1u] + 
b[1u]) o

f type float to const(_error_[])
t.d(4): no identifier for declarator c[1 - 1]
t.d(4): Error: c is used as a type
t.d(4): Error: cannot implicitly convert expression (cast(float)a[0u] + 
b[0u]) o

f type float to const(_error_[])
t.d(11): Error: mixin 
t.main.ArrayVectorOp!(+,c,a,b,3u).ArrayVectorOp!(op,c,a,

b,2).ArrayVectorOp!(op,c,a,b,1) error instantiating
t.d(11): Error: mixin 
t.main.ArrayVectorOp!(+,c,a,b,3u).ArrayVectorOp!(op,c,a,

b,2) error instantiating
t.d(18): Error: mixin t.main.ArrayVectorOp!(+,c,a,b,3u) error 
instantiating

auto arr = new int[10];

[%u]

is there any different b/w:
auto arr = new int[10];
and
int[10] arr;
?

Re: auto arr = new int[10];

[Piotr Szturmaj]

%u wrote:

is there any different b/w:
auto arr = new int[10];


arr is dynamic array of int with ten elements


and
int[10] arr;
?


arr is static array of int with ten elements

Re: Vector operations doesn't convert to a common type?

[bearophile]

simendsjo:

  int[3]   a = [1,2,4];
  float[3] b = [1,2,4];
  float[3] c;
  // Why doesn't this work?
  c = a[] + b[]; // Error: incompatible types for ((a[]) + (b[])): 
 'int[]' and 'float[]'

  // When this works?
  c[0] = a[0] + b[0];
  c[1] = a[1] + b[1];
  c[2] = a[2] + b[2];
  assert(c == [2,4,8]);

Vector ops are often implemented in assembly, and despite they are less 
flexible, they sometimes lead to more efficiency (if the arrays are large). The 
second example uses normal D code, that's much more flexible.

Bye,
bearophile

Re: A use case for fromStringz

[Andrej Mitrovic]

Yeah I basically took the idea from the existing D implementation.
Although D's arrays are a struct with a length and a pointer (I think
so).

accessing your scope for template metaprogramming ?

[Sean Cavanaugh]

Is there any way to access the your current scope?  For instance the 
following pseudocode is what I am after more or less:



class Foo
{
  alias byte function(int) BarCompatibleInterface;

  byte Bar(int)
  {
static assert(is(typeof(localscope) == function));

static assert(is(std.traits.ReturnType!(localscope) == 
std.traits.ReturnType!(BarCompatibleInterface));


static assert(is(std.traits.ParameterTypeTuple!(localscope) == 
std.traits.ParameterTypeTuple!(BarCompatibleInterface));


static assert(is(typeof(localscope.outer) == class));

static assert(is(typeof(localscope.outer.outer) == module));
  }
}


My desire for this is to help the compiler generate better error 
messages from compilation of string mixins, as they could access the 
function and/or class they are in and give a better error message from 
within a static assert() construct.

Re: accessing your scope for template metaprogramming ?

[bearophile]

Sean Cavanaugh:

 Is there any way to access the your current scope?  For instance the 
 following pseudocode is what I am after more or less:
 
 
 class Foo
 {
alias byte function(int) BarCompatibleInterface;
 
byte Bar(int)
{
  static assert(is(typeof(localscope) == function));

You have just invented another purpose for something like a _function_, that 
refers to the current function that I have originally desired to solve this 
different problem.

See my Comments 1 and 2 here:
http://d.puremagic.com/issues/show_bug.cgi?id=5140

Bye,
bearophile