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Learning Perl on Win32 Systems

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Previous: 3.1 What Is a List or Array?Chapter 3
Arrays and List Data
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3.2 Literal Representation

A list literal (the way you represent the value of a list within your program) consists of comma-separated values enclosed in parentheses. These values form the elements of the list. For example:

(1,2,3)      # array of three values 1, 2, and 3
("fred",4.5) # two values, "fred" and 4.5

The elements of a list are not necessarily constants - they can be expressions that will be evaluated newly each time the literal is used. For example:

($a, 17)      # two values: the current value of $a, and 17
($b+$c,$d+$e) # two values

The empty list (one of no elements) is represented by an empty pair of parentheses:

() # the empty list (zero elements)

An item of the list literal can include the list constructor function, indicated by two scalar values separated by two consecutive periods. This function creates a list of values starting at the left scalar value and continuing up through the right scalar value, incrementing by one at each value. For example:

(1..5)       # same as (1, 2, 3, 4, 5)
(1.2..5.2)   # same as (1.2, 2.2, 3.2, 4.2, 5.2)
(2..6,10,12) # same as (2,3,4,5,6,10,12)
($a..$b)     # range determined by current values of $a and $b

Having the right scalar less than the left scalar results in an empty list; you can't count down by switching the order of the values. If the final value is not a whole number of steps above the initial value, the list stops just before the next value would have been outside the range:

(1.3..6.1) # same as (1.3,2.3,3.3,4.3,5.3)

List literals with lots of short text strings start to look pretty noisy with all the quotes and commas:

@a = ("fred","barney","betty","wilma"); # ugh!

Fortunately, Perl has a shortcut: the "quote-word" syntax, which creates a list from the nonwhitespace parts between the parentheses:

@a = qw(fred barney betty wilma); # better!
@a = qw(
        fred
        barney
        betty
        wilma
);                                # same thing

One use of a list literal is as arguments to the print() function introduced earlier. Elements of the list are printed out without any intervening whitespace:

print("The answer is ",$a,"\n"); # three element literal array

This statement prints "The answer is" followed by a space, the value of $a, and a newline. Stay tuned for other uses for list literals.


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3.1 What Is a List or Array?Book Index3.3 Variables