Idea to modify the Point of Instantiation rule (POI)

[vasslitvinov]

One way to modify our current POI rule is to require users to opt into it. By default it would not apply. To opt in, provide some syntax to add to the call, for example akin to try-expressions or a keyword-like receiver.

proc aLibraryFunction(.....) {
  anotherLibraryFunction(...);
  userScope.aUserProvidedFunction(...);  // 'userScope' is a keyword like 'this'
}

Benefits:

• make the user aware of the POI rule
• make the uses of POI explicit
• make generic and non-generic functions uniform w.r.t. POI

No change:

• cannot require users to specify "1 caller up the call chain," "2 callers up," etc. -- that may be hard to predict and is subject to change depending how many intermediate wrappers or libraries there may be
• this rule per se does not address #6252

Downside:

• even less elegant for implicit functionality, such as initialization or assignment

  var x: T; // what syntax would indicate a request for a POI lookup of 'init()' ?

[vasslitvinov]

@mppf @bradcray @benharsh what do you think about this idea?

[mppf]

@vasslitvinov - I think this is an interesting idea but I would expect it to have different syntax. As you pointed out, we would need a way to make things like var x: T work. That leads my thinking to some kind of decorator for the function or some of its arguments or some kind of block statement.

However I think the main question here is this - is it the common case that unconstrained generics will need this behavior? In that case, what do we gain by requiring users to opt in (almost all the time)?