Simen kjaeraas:
> This is fairly simple currently:
>
> template map( alias fn ) { // blah blah blah, whatever is necessary here
> static if ( isPure!fn ) {
> pure map( Range )( Range r ) { ... }
> } else {
> auto map( Range )( Range r ) { ... }
> }
> }
Do you mean code like this (this doesn't work yet)?
import std.traits: functionAttributes, FunctionAttribute, isCallable;
import std.stdio: writeln;
pure int sqr(int x) { return x * x; }
int tot = 2;
int adder(int x) { return x + tot; } // not pure
template map(alias fn) {
static if (isPure!fn) {
pure int[] map(int[] array) {
int[] result = new int[array.length];
foreach (i, item; array)
result[i] = func(item);
return result;
}
} else {
int[] map(int[] array) {
int[] result = new int[array.length];
foreach (i, item; array)
result[i] = func(item);
return result;
}
}
}
template isPure(F) if (isCallable!(F)) {
enum bool isPure = functionAttributes!(F) & FunctionAttribute.PURE;
}
void main() {
int[] arr1 = [1, 2, 3, 4, 5];
writeln(arr1);
int[] arr2 = map!(&sqr)(arr1);
writeln(arr2);
int[] arr3 = map!(&adder)(arr1);
writeln(arr3);
//writeln(isPure!(typeof(&map!(typeof(&sqr)))));
//writeln(isPure!(typeof(&map!(typeof(&adder)))));
}
I suggest all people in all D newsgroups, to write code that runs, not
uncompilable snippets. All errors in the last Walter's talk can be avoided in
few minutes running the code. In Python newsgroups 90% of the code snippets are
run before they are shown to people.
> Of course, this leads to code duplication, which is unwanted.
You can probably remove the duplication using a mixin but this makes things
worse :-)
> In cases
> like this, I long for some features of the C preprocessor, which would
> be able to insert any kind of code wherever it wants.
It's much better to look for more clean solutions.
> This feature request, and Steve's problems with final (in
> std.pattern..mixin temptes..std.concurrency), makes me think there
> should be some way to specify all (or at least most) such conditionally.
> There seems to be a real need for it.
A silly idea to add or not add an attribute:
import std.traits: IF = Select;
IF!(isPure!TF, @pure, @nothing) int[] map(TF)(TF func, int[] array) {...}
Bye,
bearophile
