Here is an example:
int[] arr = [ 1, 2, 3, 4, 5 ];
auto foo = filter!("a < 3")(arr);
assert(foo == [ 1, 2 ]); // works fine
Now I want to be able to parameterize the predicate, e.g.
int max = 3;
int[] arr = [ 1, 2, 3, 4, 5 ];
auto foo = filter!("a < max")(arr); // doesn't compile
This snippet won't compile obviously, sine the filter!()'s predicate only accepts one parameter. Is there a way to overcome this limitation without resorting to the good ol' for/foreach loop?
The string lambdas are just a library level convenience, designed to be even terser than D's builtin function/delegate/template literals as a convenience. Here's what to do when you need more power:
Note: The following should work, but may behave erratically at the time of writing due to compiler bugs.
import std.algorithm;
void main() {
int max = 3;
int[] arr = [ 1, 2, 3, 4, 5 ];
auto foo = filter!((a) { return a < max; })(arr);
}
The following actually does work:
import std.algorithm;
void main() {
int max = 3;
int[] arr = [ 1, 2, 3, 4, 5 ];
auto foo = filter!((int a) { return a < max; })(arr);
}
The difference is whether a type is explicitly specified.