• simendsjo (11/11) Apr 16 2011 int[3] a = [1,2,4];
• simendsjo (47/58) Apr 16 2011 I tried using a template mixin to avoid having to type this all over,
• Philippe Sigaud (20/23) Apr 17 2011 Try this:
• bearophile (4/15) Apr 16 2011 Vector ops are often implemented in assembly, and despite they are less ...

simendsjo <simen.endsjo pandavre.com> writes:

     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]);

simendsjo <simen.endsjo pandavre.com> writes:

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

Philippe Sigaud <philippe.sigaud gmail.com> writes:

On Sat, Apr 16, 2011 at 13:37, simendsjo <simen.endsjo pandavre.com> wrote:
 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 :)

Try this:


auto arrayOp(string op, A, B, int N, int n = 0)(A[N] a, B[N] b)
{
    static if (n < N - 1)
        mixin("return [a[n] " ~ op ~ " b[n]] ~ arrayOp!(op,A,B,N,n+1)(a, b);");
    else
        mixin("return [a[n] " ~ op ~ " b[n]];");
}

void main()
{
    int[3]   a = [1,2,4];
    float[3] b = [1,2,4];
    auto c = arrayOp!"+"(a,b);
    writeln(c);
}

I had to resort to the N/n kludge, because of A[N] <-> A[] incompatibilities.

Note that this could easily be extend to accept any string function
(ala std.algorithm) and any number of arrays.

Philippe

bearophile <bearophileHUGS lycos.com> writes:

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