rest_pattern_microbench.dart

const count = 1000000;

bool b = false;
dynamic top;

void main() {
  var sw = Stopwatch();
  
  sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, 2, 3, ...List<int> myList, 1] when b: top = myList;
      case [1, 2, ...List<int> myList, 1] when b: top = myList;
      case [1, ...List<int> myList, 1]: top = myList;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, match 4/3/2, create 3');

  sw.reset(); sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, 2, 3, ..., 1] when b: break;
      case [1, 2, ..., 1] when b: break;
      case [1, ...List<int> myList, 1]: top = myList;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, match 4/3/2, create 1');

  sw.reset(); sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, 2, 3, ..., 1] when b: break;
      case [1, 2, ..., 1] when b: break;
      case [1, ..., 1]: break;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, match 4/3/2, create 0');

  sw.reset(); sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, ...List<int> myList, 1] when b: top = myList;
      case [1, ...List<int> myList, 1] when b: top = myList;
      case [1, ...List<int> myList, 1]: top = myList;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, create 1, get 2 from cache');

  sw.reset(); sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, ..., 1] when b: break;
      case [1, ..., 1] when b: break;
      case [1, ...List<int> myList, 1]: top = myList;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, create 1, no cache');

  sw.reset(); sw.start();
  for (int i = 0; i < count; ++i) {
    switch (<int>[1, 2, 3, i, 3, 2, 1]) {
      case [1, ..., 1] when b: break;
      case [1, ..., 1] when b: break;
      case [1, ..., 1]: break;
    }
  }
  sw.stop();
  print('Elapsed ${sw.elapsedMicroseconds}, create 0');
}

// Based on chat with Slava about the cost associated with binding rest
// patterns in list patterns: Do they have to create a new list?
//
// Trying out the cost of binding rest patterns in list patterns, do we
// actually cache the results when that would be possible?
//
// Example output from run:
/*
> dart n039.dart
head_test_dart n039.dart
Elapsed 140266, match 4/3/2, create 3
Elapsed 306814, match 4/3/2, create 1
Elapsed 20366, match 4/3/2, create 0
Elapsed 822918, create 1, get 2 from cache
Elapsed 302487, create 1, no cache
Elapsed 18273, create 0

> dart compile exe n039.dart
> ./n039.exe
Elapsed 87765, match 4/3/2, create 3
Elapsed 32439, match 4/3/2, create 1
Elapsed 541, match 4/3/2, create 0
Elapsed 32748, create 1, get 2 from cache
Elapsed 32503, create 1, no cache
Elapsed 812, create 0

> dart compile js n039.dart
> d8 out.js
Elapsed 218000, match 4/3/2, create 3
Elapsed 74000, match 4/3/2, create 1
Elapsed 9000, match 4/3/2, create 0
Elapsed 150000, create 1, get 2 from cache
Elapsed 70000, create 1, no cache
Elapsed 8000, create 0
*/
// Lessons learned from this:
//
// - 'match 4/3/2, create 1', 'create 1, get 2 from cache', 'create 1,
//   no cache' are surprisingly expensive on the VM.
// - AOT (exe) seems to work very well.
// - AOT (js) is expensive at 140000, create 1, get 2 from cache.