vandadnp / going-deep-with-dart Goto Github PK

Hi, dear Vandad!

I have some questions about the dart compilers that I thought this repository would be a great place to speak about it and document for others.

1. As you know in the dart JIT/AOT compiler we can pass definitions via --define=<key>=<value> option. Now my question is the below code snnipts.

// JIT compiler
// $ dart --define=name=ehsan main.dart
var definition = String.fromEnvironment('name');
print(definition); // ehsan

but in AOT compilation value isn't accessible, if the variable type qualifier be var and should be const

// AOT compiler
// $ dart compile exe --define=name=ehsan -o main main.dart; ./main
var definition = String.fromEnvironment('name'); // also `bool.hasEnvironment('name')` returns false
print(definition); // '' empty String, false boolean, 0 int

Actully my question is what happen in generated code that makes this difference in AOT and JIT compilation?

2. Is platform checking will happen in runtime? (in AOT compilation)

// the is<platform> static variables also use this getter
 switch (Platform.operatingSystem) {
   case 'linux':
     // do something linux
     break;
   case 'macos':
     // do something in mac
     break;
   // and so on...
 }

The section for loops over variable iterables misinterprets the meaning of call qword [rax+rcx*8+0x60], this is how interface calls work in the code produced by Dart AOT compiler. We use an approach called "global dispatch table". In the sequence above rax would be a pointer to the dispatch table, rcx would be class id of the receiver object and 0x60 is a selector id (which determines which virtual method we are looking up).

Based on the call sequence I'd say this is an invocation of get current on the iterator object which is implicitly created by the for-in loops.

https://github.com/vandadnp/going-deep-with-dart/blob/main/issue-3-for-loop-in-dart/issue-3-for-loop-in-dart.md#non-entry-for-loops-with-const-startend-values
it says it's declared with const constructors but none are present in the snippet.