Perl References

Perl References

I’m happiest writing Perl code that does not use references because they always give me a mild headache. Here’s the short version of how they work. The backslash operator () computes a reference to something. The reference is a scalar that points to the original thing. The ‘$’ dereferences to access the original thing. Suppose there is a string…

$str = “hello”; ## original string

And there is a reference that points to that string…

$ref = $str; ## compute $ref that points to $str

The expression to access $str is $$ref. Essentially, the alphabetic part of the variable, ‘str’, is replaced with the dereference expression ‘$ref’…

print “$$refn”; ## prints “hello” — identical to “$strn”;

Here’s an example of the same principle with a reference to an array…

@a = (1, 2, 3); ## original array

$aRef = @a; ## reference to the array

print “a: @an”; ## prints “a: 1 2 3”

print “a: @$aRefn”; ## exactly the same

Curly braces { } can be added in code and in strings to help clarify the stack of @, $, …

print “a: @{$aRef}n”; ## use { } for clarity

Here’s how you put references to arrays in another array to make it look two dimensional…

@a = (1, 2, 3); @b = (4, 5, 6);

@root = (@a, @b);

print “a: @an”; ## a: (1 2 3)

print “a: @{$root[0]}n”; ## a: (1 2 3)

print “b: @{$root[1]}n”; ## b: (4 5 6)

scalar(@root) ## root len == 2

scalar(@{$root[0]}) ## a len: == 3

For arrays of arrays, the [ ] operations can stack together so the syntax is more C like…

$root[1][0] ## this is 4

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