Mastering Modern Perl: Writing Efficient and Maintainable Code/

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Types of Scope II

Types of Scope II

Learn more types of scope in Perl.

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Dynamic scope

Dynamic scope resembles lexical scope in its visibility rules. Still, instead of looking outward in compile-time scopes, lookup traverses backward through all of the function calls we’ve made to reach the current code. Dynamic scope applies only to global and package global variables (since lexicals aren’t visible outside their scopes). While a global package variable may be visible within all scopes, its value may change depending on localization and assignment:

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our $scope;
sub inner {
    say $scope;
}
sub main {
    say $scope;
    local $scope = 'main() scope';
    middle();
}
sub middle {
    say $scope;
    inner();
}
$scope = 'outer scope';
main();
say $scope;

The program begins by declaring our variable, $scope, and three functions. It ends by assigning to $scope and calling main().

Within main(), the program prints the current value of $scope, outer scope, and then localizes the variable. This changes the symbol’s visibility within the current lexical scope and in any functions called from the current lexical scope; that is ...