How to modify the `print` function in Dart?

The print function is defined in both these files:

>flutter/bin/cache/pkg/sky_engine/lib/core/print.dart
>
>flutter/bin/cache/dart-sdk/lib/core/print.dart

I opened each of them and modified the function to add this line at the start

if (kDebugMode) return;

I restarted the IDE, run the app with this code

print(kDebugMode); // Prints true

The print function shouldn't have printed anything. If I go and check the implementation of those print function, my if condition line is still there.

So, what am I doing wrong?

You probably don't want to modify the source code anyway.
Instead, you can use Zone to override the print behavior in your code without modifying the SDK.

You can do:

import 'dart:async';

void main() {
  runZoned(
    () => print('Hello world'),
    zoneSpecification: ZoneSpecification(
      print: (self, parent, zone, line) {
        // Your logic here:
        // if (kDebugMode) return;
        // Now use the original print implementation:
        parent.print(zone, 'This is a custom print: $line');
      },
    ),
  );
}

This example overrides print to customize the output. In this example, even though we called print('Hello world'), the output will be This is a custom print: Hello world