Issue #17474 has been updated by Dan0042 (Daniel DeLorme).


Some time ago I thought of basically the same idea, but in the end decided that constants were the appropriate way to handle this, so I didn't make it a proposal.
	
But the cases presented by Marc-Andre are remarkably compelling. It's the first time I hear about the Regexp `o` modifier, but deduplicated strings have a similar function to this proposal, and Array literals would benefit from that kind of optimization too, not to mention Sets as proposed in #16994.

So this proposal can "unify" various proposals and parts of the language into a single reusable concept, and I find that's usually the sign there's something very worthwhile here.

Let's say that we use `$(expr)` to denote these "global single-eval expressions", and of course they have to be made ractor-shareable as Marc-Andre pointed out. So instead of introducing multiple special-case syntaxes for basically the same purpose, we could have something like:

```
$(/#{1+2}/)                     #equivalent /#{1+2}/o
$("foo")                        #equivalent to -"foo" or "foo".freeze
$(%w[x y z]).include?(v)
$(Set["x","y","z"]).include?(v)
```

Yes, I'm warming up to the idea.

----------------------------------------
Feature #17474: Interpreting constants at compile time
https://bugs.ruby-lang.org/issues/17474#change-89592

* Author: jzakiya (Jabari Zakiya)
* Status: Open
* Priority: Normal
----------------------------------------
Ruby has borrowed concepts/idioms from allot of languages.

I am proposing borrowing a feature from Forth to provide for compile time interpretation of Constants.
This should make executed code faster|efficient, while maintaining source code brevity|clarity.

Below is actual code used in a large rubygem I have.

To develop this method, I had to do allot of test runs to determine the range values.
Once found, these values don't change, but I just kept the computed forms of the values, in case I want to upgrade them.
In Forth I can interpret those expressions that result in constants, which will be compiled as single values for run time.

See wikeipedia article on Forth below starting at **Mixing states of compiling and interpreting**.
https://en.wikipedia.org/wiki/Forth_(programming_language)

Forth was designed for, and is still used most frequently, in hardware controllers, and with microprocessors.
IMHO this feature would also make MRuby more code efficient and faster for this domain too, and IOT devices.

Below is an example of real code that would benefit from this.
While this example would result in numerical constant, string constants could also be interpreted.

```
def select_pg(endnum, startnum)
  start_num = end_num 
  end_num = endnum;  start_num = startnum
  range = end_num - start_num
  pg = 5
  if start_num <= Integer.sqrt(end_num)  # for one array of primes upto N
    pg =  7 if end_num >  50 * 10**4
    pg = 11 if end_num > 305 * 10**5
  else                                   # for split array cases
    pg =  7 if ((10**6 ... 10**7).include?(range) && start_num < 10**8)       ||
               ((10**7 ... 10**8).include?(range) && start_num < 46 * 10**8)  ||
               ((10**8 ... 10**9).include?(range) && start_num < 16 * 10**10) ||
               (range >= 10**9 && start_num < 26 * 10**12)        
    pg = 11 if ((10**8 ... 10**9).include?(range) && start_num < 55 * 10**7)  ||
               (range >= 10**9 && start_num < 45 * 10**9)
  end
  primes = [2, 3, 5, 7, 11, 13].select { |p| p <= pg }
  {primes, primes.reduce(:*)}            # [excluded primes, modpg] for PG
end
```
Allowing for compile time interpretation, the code could be rewritten as below.

```
def select_pg(endnum, startnum)
  start_num = end_num 
  end_num = endnum;  start_num = startnum
  range = end_num - start_num
  pg = 5
  if start_num <= Integer.sqrt(end_num)  # for one array of primes upto N
    pg =  7 if end_num >  [50 * 10**4]
    pg = 11 if end_num > [305 * 10**5]
  else                                   # for split array cases
    pg =  7 if (([10**6] ... [10**7]).include?(range) && start_num < [10**8])      ||
               (([10**7] ... [10**8]).include?(range) && start_num < [46 * 10**8]) ||
               (([10**8] ... [10**9]).include?(range) && start_num < [16 * 10**10])|| 
               (range >= [10**9] && start_num < [26 * 10**12])        
    pg = 11 if (([10**8] ... [10**9]).include?(range) && start_num < [55 * 10**7]) ||
               (range >= [10**9] && start_num < [45 * 10**9])
  end
  primes = [2, 3, 5, 7, 11, 13].select { |p| p <= pg }
  {primes, primes.reduce(:*)}            # [excluded primes, modpg] for PG
end

```
This maintains the original form, so if I need/want to change the range limits again
I can just change the calculation inline, without having to remember where those values came from.

As 3.0 has introduced many new features and idioms, this could be introduced with no breaking change too.
Old code would work as before, while new code could take advantage of this feature.

Thanks is advance of giving this proposal serious consideration.




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