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Perl 5.6.1 and newer support autovivification of file and directory handles. [3] Calling open() on an undefined variable will set it to a filehandle. According to perl561delta, "[t]his largely eliminates the need for typeglobs when opening filehandles that must be passed around, as in the following example:
The empty hash {} is also true; in this context {} is not an empty block, because perl -e 'print ref {}' returns HASH. Evaluated boolean expressions are also scalar values. The documentation does not promise which particular value of true or false is returned. Many boolean operators return 1 for true and the empty-string for false.
A hash literal is a key-value list, with the preferred form using Perl's => token, which is semantically mostly identical to the comma and makes the key-value association clearer: my %phone_book = ( 'Sally Smart' => '555-9999' , 'John Doe' => '555-1212' , 'J. Random Hacker' => '553-1337' , );
It is primarily associated with PHP, Ruby and Perl programming languages, which use it to declare hashes. Using a fat comma to bind key-value pairs in a hash, instead of using a comma, is considered an example of good idiomatic Perl. [1] In CoffeeScript and TypeScript, the fat comma is used to declare a function that is bound to this. [2] [3]
In hash-based fingerprints, a hash function based on atom and bond properties is used to turn a subgraph into a PRNG seed, and the first output values used to set bits in the Bloom filter. Molecular fingerprints started in the late 1940s as way to search for chemical structures searched on punched cards.
Perl provides three loop control keywords that all accept an optional loop label as an argument. If no label is specified, the keywords act on the innermost loop. Within nested loops, the use of labels enables control to move from an inner loop to an outer one, or out of the outer loop altogether.
In computer science, a hash table is a data structure that implements an associative array, also called a dictionary or simply map; an associative array is an abstract data type that maps keys to values. [2] A hash table uses a hash function to compute an index, also called a hash code, into an array of buckets or slots, from which the desired ...
[3] [4] [5] [11] In separate chaining, the array does not store the value itself but stores a pointer to another container, usually an association list, that stores all the values matching the hash. By contrast, in open addressing, if a hash collision is found, the table seeks an empty spot in an array to store the value in a deterministic ...