Programming Perl, 4th Edition

Space Efficiency

• Give variables the shortest scope possible so they don’t take up space when they aren’t needed.

• Use vec for compact integer array storage if the integers are of fixed width. (Integers of variable width can be stored in a UTF-8 string.)

• Prefer numeric values over equivalent string values; they require less memory.

• Use substr to store constant-length strings in a longer string.

• Use the Tie::SubstrHash module for very compact storage of a hash array if the key and value lengths are fixed.

• Use _ _END_ _ and the DATA filehandle to avoid storing program data as both a string and an array.

• Prefer each to keys where order doesn’t matter.

• Delete or undef globals that are no longer in use.

• Use some kind of DBM to store hashes on disk instead of inside the program.

• Use temp files to store arrays.

• Use pipes to offload processing to other tools. They clean up their memory use when they exit.

• Avoid list operations and entire file slurps.

• Avoid using tr///. Each tr/// expression must store a sizable translation table.

• Don’t unroll your loops or inline your subroutines.

• Use File::Map to read files if you don’t need to modify the data (and sometimes even if you do).

• Avoid recursion. Perl doesn’t have tail-call optimization since it’s a dynamic language. You should be able to convert those to an iterative approach, which is how languages with tail-call optimize recursion.