Ways in which this module applies this rule.

By default, this rule is relaxed in that 2 is permitted to allow for common things like alternation, the STDERR file handle, etc..

Numeric literals are allowed in "use" and "require" statements to allow for things like Perl version restrictions and Test::More plans. Declarations of $VERSION package variables are permitted. Use of "Readonly", "Readonly::Scalar", "Readonly::Array", and "Readonly::Hash" from the Readonly module are obviously valid, but use of "Readonly::Scalar1", "Readonly::Array1", and "Readonly::Hash1" are specifically not supported.

Use of binary, exponential, hexadecimal, octal, and version numbers, even for 0 and 1, outside of "use"/"require"/"Readonly" statements aren't permitted (but you can change this).

There is a special exemption for accessing the last element of an array, i.e. $x[-1].

    $x = 0;                                   # ok
    $x = 0.0;                                 # ok
    $x = 1;                                   # ok
    $x = 1.0;                                 # ok
    $x = 1.5;                                 # not ok
    $x = 0b0                                  # not ok
    $x = 0b1                                  # not ok
    $x = 0x00                                 # not ok
    $x = 0x01                                 # not ok
    $x = 000                                  # not ok
    $x = 001                                  # not ok
    $x = 0e1                                  # not ok
    $x = 1e1                                  # not ok
    $frobnication_factor = 42;                # not ok
    use constant FROBNICATION_FACTOR => 42;   # ok
    use 5.6.1;                                # ok
    use Test::More plan => 57;                # ok
    plan tests => 39;                         # ok
    our $VERSION = 0.22;                      # ok
    $x = $y[-1]                               # ok
    $x = $y[-2]                               # not ok
    foreach my $solid (1..5) {                # not ok
        ...
    }
    use Readonly;
    Readonly my $REGULAR_GEOMETRIC_SOLIDS => 5;
    foreach my $solid (1..$REGULAR_GEOMETRIC_SOLIDS) {  #ok
        ...
    }

"allowed_values"

The "allowed_values" parameter is a whitespace delimited set of permitted number values; this does not affect the permitted formats for numbers. The defaults are equivalent to having the following in your .perlcriticrc:

    [ValuesAndExpressions::ProhibitMagicNumbers]
    allowed_values = 0 1 2

Note that this policy forces the values 0 and 1 into the permitted values. Thus, specifying no values,

    allowed_values =

is the same as simply listing 0 and 1:

    allowed_values = 0 1

The special "all_integers" value, not surprisingly, allows all integral values to pass, subject to the restrictions on number types.

Ranges can be specified as two (possibly fractional) numbers separated by two periods, optionally suffixed with an increment using the Perl 6 ":by()" syntax. E.g.

    allowed_values = 7..10

will allow 0, 1, 7, 8, 9, and 10 as literal values. Using fractional values like so

    allowed_values = -3.5..-0.5:by(0.5)

will permit -3.5, -3, -2.5, -2, -2.5, -1, -0.5, 0, and 1. Unsurprisingly, the increment defaults to 1, which means that

    allowed_values = -3.5..-0.5

will make -3.5, -2.5, -2.5, -0.5, 0, and 1 valid.

Ranges are not lazy, i.e. you'd better have a lot of memory available if you use a range of "1..1000:by(0.01)". Also remember that all of this is done using floating-point math, which means that "1..10:by(0.3333)" is probably not going to be very useful.

Specifying an upper limit that is less than the lower limit will result in no values being produced by that range. Negative increments are not permitted.

Multiple ranges are permitted.

To put this all together, the following is a valid, though not likely to be used, .perlcriticrc entry:

    [ValuesAndExpressions::ProhibitMagicNumbers]
    allowed_values = 3.1415269 82..103 -507.4..57.8:by(0.2) all_integers

"allowed_types"

The "allowed_types" parameter is a whitespace delimited set of subclasses of PPI::Token::Number.

Decimal integers are always allowed. By default, floating-point numbers are also allowed.

For example, to allow hexadecimal literals, you could configure this policy like

    [ValuesAndExpressions::ProhibitMagicNumbers]
    allowed_types = Hex

but without specifying anything for "allowed_values", the allowed hexadecimal literals will be 0x00, 0x01, and 0x02. Note, also, as soon as you specify a value for this parameter, you must include "Float" in the list to continue to be able to use floating point literals. This effect can be used to restrict literals to only decimal integers:

    [ValuesAndExpressions::ProhibitMagicNumbers]
    allowed_types =

If you permit exponential notation, you automatically also allow floating point values because an exponential is a subclass of floating-point in PPI.

"allow_to_the_right_of_a_fat_comma"

If this is set, you can put any number to the right of a fat comma.

    my %hash =     ( a => 4512, b => 293 );         # ok
    my $hash_ref = { a => 4512, b => 293 };         # ok
    some_subroutine( a => 4512, b => 293 );         # ok

Currently, this only means directly to the right of the fat comma. By default, this value is true.

"constant_creator_subroutines"

This parameter allows you to specify the names of subroutines that create constants, in addition to "Readonly", "Const::Fast", and friends. For example, if you use a custom "Const::Fast"-like module that supports a "create_constant" subroutine to create constants, you could add something like the following to your .perlcriticrc:

    [ValuesAndExpressions::ProhibitMagicNumbers]
    constant_creator_subroutines = create_constant

If you have more than one name to add, separate them by whitespace.

The subroutine name should appear exactly as it is in your code. For example, if your code does not import the creating subroutine subroutine, you would need to configure this policy as something like

    [ValuesAndExpressions::ProhibitMagicNumbers]
    constant_creator_subroutines = create_constant Constant::Create::create_constant