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Pre-RFC Deep constants

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Robert Rothenberg
March 9, 2023 16:58
Pre-RFC Deep constants
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I'm a fan of using constants in code, and often using interpolatable 
constants with something like Readonly or Const::Fast for deep constants:

But it would be nice to have a way to specify deep constants without 
having to use one of several non-core modules, perhaps allowing the 
compiler to optimize code knowing that certain things are constants.

It would also be nice to create state variable constants without 
restoring to weird hackery to check if the state is defined, e.g. the 
following fails:

     use Const::Fast;

     for (1..2) {

         const state $var => { a => "something", b => 2 };


I'm still thinking about what the better syntax is. Some ideas,

1. A constant keyword akin to Const::Fast,

   const my $var = ....

This has the advantage of letting devs specify the lexical scope  the 
variable, e.g. "our", "my" or "state".

2. An attribute

   my $var :readonly = ....

3. A special function

   my $var = readonly( ... )

There are some other questions:

- Do we want to have separate keywords or options for deep vs shallow 

- Do we want the ability to have write-once values?

- How do we handle blessed references? Do we skip them silently? Throw 
an exception? Or mark them as read only?

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