1Number::Tolerant(3)   User Contributed Perl Documentation  Number::Tolerant(3)
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NAME

6       Number::Tolerant - tolerance ranges for inexact numbers
7

VERSION

9       version 1.708
10

SYNOPSIS

12        use Number::Tolerant;
13
14        my $range  = tolerance(10 => to => 12);
15        my $random = 10 + rand(2);
16
17        die "I shouldn't die" unless $random == $range;
18
19        print "This line will always print.\n";
20

DESCRIPTION

22       Number::Tolerant creates a number-like object whose value refers to a
23       range of possible values, each equally acceptable.  It overloads
24       comparison operations to reflect this.
25
26       I use this module to simplify the comparison of measurement results to
27       specified tolerances.
28
29        reject $product unless $measurement == $specification;
30

METHODS

32   Instantiation
33       new
34
35       tolerance
36
37       There is a "new" method on the Number::Tolerant class, but it also
38       exports a simple function, "tolerance", which will return an object of
39       the Number::Tolerant class.  Both use the same syntax:
40
41        my $range = Number::Tolerant->new( $x => $method => $y);
42
43        my $range = tolerance( $x => $method => $y);
44
45       The meaning of $x and $y are dependent on the value of $method, which
46       describes the nature of the tolerance.  Tolerances can be defined in
47       five ways, at present:
48
49         method              range
50        -------------------+------------------
51         plus_or_minus     | x +/- y
52         plus_or_minus_pct | x +/- (y% of x)
53         or_more           | x to Inf
54         or_less           | x to -Inf
55         more_than         | x to Inf, not x
56         less_than         | x to -Inf, not x
57         to                | x to y
58         infinite          | -Inf to Inf
59         offset            | (x + y1) to (x + y2)
60
61       For "or_less" and "or_more", $y is ignored if passed.  For "infinite",
62       neither $x nor $y is used; "infinite" should be the sole argument.  The
63       first two arguments can be reversed for "more_than" and "less_than", to
64       be more English-like.
65
66       Offset tolerances are slightly unusual.  Here is an example:
67
68         my $offset_tolerance = tolerance(10 => offset => (-3, 5));
69         # stringifies to: 10 (-3 +5)
70
71       An offset is very much like a "plus_or_minus" tolerance, but its center
72       value is not necessarily the midpoint between its extremes.  This is
73       significant for comparisons and numifications of the tolerance.  Given
74       the following two tolerances:
75
76         my $pm_dice = tolerance(10.5 => plus_or_minus => 7.5);
77         my $os_dice = tolerance(11 => offset => (-8, 7));
78
79       The first will sort as numerically less than the second.
80
81       If the given arguments can't be formed into a tolerance, an exception
82       will be raised.
83
84       from_string
85
86       A new tolerance can be instantiated from the stringification of an old
87       tolerance.  For example:
88
89        my $range = Number::Tolerant->from_string("10 to 12");
90
91        die "Everything's OK!" if 11 == $range; # program dies of joy
92
93       This will not yet parse stringified unions, but that will be
94       implemented in the future.  (I just don't need it yet.)
95
96       If a string can't be parsed, an exception is raised.
97
98   stringify_as
99         my $string = $tolerance->stringify_as($type);
100
101       This method does nothing!  Someday, it will stringify the given
102       tolerance as a different type, if possible.  "10 +/- 1" will
103       "stringify_as('plus_or_minus_pct')" to "10 +/- 10%" for example.
104
105   numify
106         my $n = $tolerance->numify;
107
108       This returns the numeric form of a tolerance.  If a tolerance has both
109       a minimum and a maximum, and they are the same, then that is the
110       numification.  Otherwise, numify returns undef.
111
112   Overloading
113       Tolerances overload a few operations, mostly comparisons.
114
115       boolean
116           Tolerances are always true.
117
118       numify
119           Most tolerances numify to undef; see "numify".
120
121       stringify
122           A tolerance stringifies to a short description of itself, generally
123           something like "m < x < n"
124
125            infinite  - "any number"
126            to        - "m <= x <= n"
127            or_more   - "m <= x"
128            or_less   - "x <= n"
129            more_than - "m < x"
130            less_than - "x < n"
131            offset    - "x (-y1 +y2)"
132            constant  - "x"
133            plus_or_minus     - "x +/- y"
134            plus_or_minus_pct - "x +/- y%"
135
136       equality
137           A number is equal to a tolerance if it is neither less than nor
138           greater than it.  (See below).
139
140       smart match
141           Same as equality.
142
143       comparison
144           A number is greater than a tolerance if it is greater than its
145           maximum value.
146
147           A number is less than a tolerance if it is less than its minimum
148           value.
149
150           No number is greater than an "or_more" tolerance or less than an
151           "or_less" tolerance.
152
153           "...or equal to" comparisons include the min/max values in the
154           permissible range, as common sense suggests.
155
156       tolerance intersection
157           A tolerance "&" a tolerance or number is the intersection of the
158           two ranges.  Intersections allow you to quickly narrow down a set
159           of tolerances to the most stringent intersection of values.
160
161            tolerance(5 => to => 6) & tolerance(5.5 => to => 6.5);
162            # this yields: tolerance(5.5 => to => 6)
163
164           If the given values have no intersection, "()" is returned.
165
166           An intersection with a normal number will yield that number, if it
167           is within the tolerance.
168
169       tolerance union
170           A tolerance "|" a tolerance or number is the union of the two.
171           Unions allow multiple tolerances, whether they intersect or not, to
172           be treated as one.  See Number::Tolerant::Union for more
173           information.
174

EXTENDING

176       This feature is slighly experimental, but it's here.
177
178       New tolerance types may be written as subclasses of
179       Number::Tolerant::Type, providing the interface described in its
180       documentation.  They can then be enabled or disabled with the following
181       methods:
182
183   " enable_plugin "
184         Number::Tolerant->enable_plugin($class_name);
185
186       This method enables the named class, so that attempts to create new
187       tolerances will check against this class.  Classes are checked against
188       "validate_plugin" before being enabled.  An exception is thrown if the
189       class does not appear to provide the Number::Tolerant::Type interface.
190
191   " disable_plugin "
192         Number::Tolerant->disable_plugin($class_name);
193
194       This method will disable the named class, so that future attempts to
195       create new tolerances will not check against this class.
196
197   " validate_plugin "
198         Number::Tolerant->validate_plugin($class_name);
199
200       This method checks (naively) that the given class provides the
201       interface defined in Number::Tolerant::Type.  If it does not, an
202       exception is thrown.
203

TODO

205       •   Extend "from_string" to cover unions.
206
207       •   Extend "from_string" to include Number::Range-type specifications.
208
209       •   Allow translation into forms not originally used:
210
211            my $range    = tolerance(9 => to => 17);
212            my $range_pm = $range->convert_to('plus_minus');
213            $range->stringify_as('plus_minus_pct');
214
215       •   Create a factory so that you can simultaneously work with two sets
216           of plugins.
217
218           This one is very near completion.  There will now be two classes
219           that should be used:  Number::Tolerant::Factory, which produces
220           tolerances, and Number::Tolerant::Tolerance, which is a tolerance.
221           Both will inherit from N::T, for supporting old code, and N::T will
222           dispatch construction methods to a default factory.
223

SEE ALSO

225       The module Number::Range provides another way to deal with ranges of
226       numbers.  The major differences are: N::R is set-like, not range-like;
227       N::R does not overload any operators.  Number::Tolerant will not (like
228       N::R) attempt to parse a textual range specification like
229       "1..2,5,7..10" unless specifically instructed to.  (The valid formats
230       for strings passed to "from_string" does not match Number::Range
231       exactly.  See TODO.)
232
233       The "Number::Range" code:
234
235        $range = Number::Range->new("10..15","20..25");
236
237       Is equivalent to the "Number::Tolerant" code:
238
239        $range = Number::Tolerant::Union->new(10..15,20..25);
240
241       ...while the following code expresses an actual range:
242
243        $range = tolerance(10 => to => 15) | tolerance(20 => to => 25);
244

THANKS

246       Thanks to Yuval Kogman and #perl-qa for helping find the bizarre bug
247       that drove the minimum required perl up to 5.8
248
249       Thanks to Tom Freedman, who reminded me that this code was fun to work
250       on, and also provided the initial implementation for the offset type.
251

AUTHOR

253       Ricardo Signes <rjbs@cpan.org>
254

CONTRIBUTORS

256       •   Alexandre Mestiashvili <alex@biotec.tu-dresden.de>
257
258       •   Karen Etheridge <ether@cpan.org>
259
260       •   Michael Carman <mjcarman@cpan.org>
261
262       •   Ricardo SIGNES <rjbs@codesimply.com>
263
264       •   Smylers <Smylers@stripey.com>
265
267       This software is copyright (c) 2004 by Ricardo Signes.
268
269       This is free software; you can redistribute it and/or modify it under
270       the same terms as the Perl 5 programming language system itself.
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274perl v5.32.1                      2021-01-27               Number::Tolerant(3)
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