Implementation for init=

[benharsh]

This PR implements support for the new kind of copy initializer, named "init=". This copy initializer will follow similar rules as a regular initializer (e.g. initialize fields in order). The init= method will be invoked for compiler-inserted copies of records, and for initialization of variables from an expression. A simple case is initializing from the same type:

var orig : MyRecord;
var copy : MyRecord = orig; // copy.init=(orig)

A more interesting case is when initializing from a different type:

record R {
  var x : int;

  proc init=(other : int) {
    this.x = other;
  }
}

var r : R = 5; // r.init=(5);

Generic types require an additional type formal that represents the intended instantiation:

record R {
  type T;
  var x : T;

  proc init=(type ThisType, other : ThisType.T) {
    this.T = ThisType.T;
    this.x = other;
  }
}

var x : R(int) = 5;
var y : R(string) = "hello";

As a result of this functionality, atomic variables can be initialized from values:

var x : atomic int = 5;

This PR allows for the old-style copy initializers to still be invoked, unless the user has implemented their own init= methods.

Testing:

• local
• memleaks
• valgrind
• gasnet

[benharsh]

This PR updates the "records.chpl" primer to use init=, but would pass if we used the old-style copy initializer. Do we want to make this change where users would see it?

[mppf]

Looking good to me. I had some questions and relatively minor feedback. Thanks!

Also do you know if we have any tests/futures of init= than use the in intent? Arguably that creates an infinite loop in compilation (since the in intent would normally mean copy-initializing, right?) but if somebody is confused it'd be nice if we gave a reasonable error.

[mppf]

These adjustments seem strange to me since I consider init= a kind of initializer. Maybe there's a way to rename isInitializer to make it less confusing. That would be reasonable to create a future work issue about.

[mppf]

This change occurs enough in this PR that I'm starting to think it'd be worth adding FnSymbol::isCopyOrRegularInit or something like that...

[benharsh]

I would like something like this too, and something that would handle the strcmp cases too. Do you want that to be done for this PR?

[mppf]

Only if you think it'll help you get the code correct. If you choose to put it off, let's make an issue and put it to get worked on soon.