ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
10.3. Creating Persistent Private VariablesProblemYou want a variable to retain its value between calls to a subroutine but not be visible outside that routine. For instance, you'd like your function to keep track of how many times it was called. SolutionWrap the function in another block, and declare { my $variable; sub mysub { # ... accessing $variable } } If the variables require initialization, make that block a BEGIN so the variable is guaranteed to be set before the main program starts running: BEGIN { my $variable = 1; # initial value sub othersub { # ... accessing $variable } } DiscussionUnlike local variables in C or C++, Perl's lexical variables don't necessarily get recycled just because their scope has exited. If something more permanent is still aware of the lexical, it will stick around. In this case, Here's how to write a counter: { my $counter; sub next_counter { return ++$counter } } Each time Generally, you should use a BEGIN for the extra scope. Otherwise, you could call the function before its variable were initialized. BEGIN { my $counter = 42; sub next_counter { return ++$counter } sub prev_counter { return --$counter } } This technique creates the Perl equivalent of C's static variables. Actually, it's a little better. Rather than being limited to just one function, both functions share their private variable. See AlsoThe section on "Closures" in Chapter 4and on "Package Constructors and Destructors: BEGIN and END" in Chapter 5 of Programming Perl; the section on "Private Variables via my( )" in perlsub (1); the section on "Package Constructors and Destructors" in perlmod (1); Recipe 11.4 |