Re: advent of code day 11

[Stephen Leake <stephen_leake@stephe-leake.org>]

John Perry <john.perry@usm.edu> writes:

> On Friday, December 11, 2020 at 11:08:00 AM UTC-6, Stephen Leake wrote:
>> mildly interesting; variation on Conway's Game of Life. 
>
> I thought it would be clearer to use references to switch from one
> chart to the other, but I had trouble doing that last night. Now I can
> get it this way:
>
>    Source: Chart_Array renames Chart1;
>    Result: Chart_Array renames Chart2;

A 'renames' declaration creates a _static_ name for the object that is
the result of the expression; the expression is evaluated once when the
'renames' declaration is evaluated. When the name is used, it is the
same as any other object name.

>    while Changed loop
>
>       Perform_Round( Source => Source , Result => Result , ... );
>       declare Tmp: Chart_Array renames Source;

'Tmp' is evaluated each time around the loop, but since the global
Source is static, it always has the same value of Chart1.

>       begin Source := Result;

This does not revaluate the expression for global Source; it uses the
global Source name to determine where to store a copy of Result.

-- 
-- Stephe