Step by Step solution about How to resolve the algorithm History variables step by step in the Ruby programming language

The provided Ruby code demonstrates the use of the trace_var method to track changes to a global variable, $foo. Here's a step-by-step breakdown of what the code does:

1. Variable Initialization: An empty array, foo_hist, is initialized to store the historical values of $foo.

2. Trace Variable: The trace_var method is invoked with :$foo as an argument. This method allows you to trace changes to a specific variable. The provided block is executed every time the value of $foo is modified.

3. Block Execution: Within the block, the current value of $foo is passed as the v parameter. The value of v is then unshifted (added to the beginning) of the foo_hist array. This effectively tracks the sequence of values assigned to $foo.

4. Variable Assignments: Subsequently, the value of $foo is modified three times by assigning the strings "apple," "pear," and "banana" to it.

5. Printing History: Finally, the foo_hist array is printed, which contains the historical values of $foo in reverse chronological order.

In summary, this code utilizes the trace_var method to keep a record of all changes made to the global variable $foo. It allows for easy tracking and retrieval of the variable's history.

foo_hist = []
trace_var(:$foo){|v| foo_hist.unshift(v)}

$foo = "apple"
$foo = "pear"
$foo = "banana"

p foo_hist # => ["banana", "pear", "apple"]