1Template::Alloy::OperatUosre(r3)Contributed Perl DocumenTteamtpiloante::Alloy::Operator(3)
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NAME

6       Template::Alloy::Operator - Operator role.
7

DESCRIPTION

9       The Template::Alloy::Operator role provides the regexes necessary for
10       Template::Alloy::Parse to parse operators and place them in their
11       appropriate precedence.  It also provides the play_operator method
12       which is used by Template::Alloy::Play and Template::Alloy::Compile for
13       playing out the stored operator ASTs.
14

ROLE METHODS

16       play_operator
17           Takes an operator AST in the form of
18
19               [undef, '+', 1, 2]
20
21           Essentially, all operators are stored in RPN notation with a
22           leading "undef" to disambiguate operators in a normal Alloy
23           expression AST.
24
25       define_operator
26           Used for defining new operators.
27
28           See Template::Alloy for more details.
29

OPERATOR LIST

31       The following operators are available in Template::Alloy.  Except where
32       noted these are the same operators available in TT.  They are listed in
33       the order of their precedence (the higher the precedence the tighter it
34       binds).
35
36       "." The dot operator.  Allows for accessing sub-members, methods, or
37           virtual methods of nested data structures.
38
39               my $obj->process(\$content, {a => {b => [0, {c => [34, 57]}]}}, \$output);
40
41               [% a.b.1.c.0 %] => 34
42
43           Note: on access to hashrefs, any hash keys that match the sub key
44           name will be used before a virtual method of the same name.  For
45           example if a passed hash contained pair with a keyname "defined"
46           and a value of "2", then any calls to hash.defined(another_keyname)
47           would always return 2 rather than using the vmethod named
48           "defined."  To get around this limitation use the "|" operator
49           (listed next).  Also - on objects the "." will always try and call
50           the method by that name.  To always call the vmethod - use "|".
51
52       "|" The pipe operator.  Similar to the dot operator.  Allows for
53           explicit calling of virtual methods and filters (filters are
54           "merged" with virtual methods in Template::Alloy and TT3) when
55           accessing hashrefs and objects.  See the note for the "." operator.
56
57           The pipe character is similar to TT2 in that it can be used in
58           place of a directive as an alias for FILTER.  It similar to TT3 in
59           that it can be used for virtual method access.  This duality is one
60           source of difference between Template::Alloy and TT2 compatibility.
61           Templates that have directives that end with a variable name that
62           then use the "|" directive to apply a filter will be broken as the
63           "|" will be applied to the variable name.
64
65           The following two cases will do the same thing.
66
67               [% foo | html %]
68
69               [% foo FILTER html %]
70
71           Though they do the same thing, internally, foo|html is stored as a
72           single variable while "foo FILTER html" is stored as the variable
73           foo which is then passed to the FILTER html.
74
75           A TT2 sample that would break in Template::Alloy or TT3 is:
76
77               [% PROCESS foo a = b | html %]
78
79           Under TT2 the content returned by "PROCESS foo a = b" would all be
80           passed to the html filter.  Under Template::Alloy and TT3, b would
81           be passed to the html filter before assigning it to the variable
82           "a" before the template foo was processed.
83
84           A simple fix is to do any of the following:
85
86               [% PROCESS foo a = b FILTER html %]
87
88               [% | html %][% PROCESS foo a = b %][% END %]
89
90               [% FILTER html %][% PROCESS foo a = b %][% END %]
91
92           This shouldn't be too much hardship and offers the great return of
93           disambiguating virtual method access.
94
95       "\" Unary.  The reference operator.  Not well publicized in TT.  Stores
96           a reference to a variable for use later.  Can also be used to
97           "alias" long names.
98
99               [% f = 7 ; foo = \f ; f = 8 ; foo %] => 8
100
101               [% foo = \f.g.h.i.j.k; f.g.h.i.j.k = 7; foo %] => 7
102
103               [% f = "abcd"; foo = \f.replace("ab", "-AB-") ; foo %] => -AB-cd
104
105               [% f = "abcd"; foo = \f.replace("bc") ; foo("-BC-") %] => a-BC-d
106
107               [% f = "abcd"; foo = \f.replace ; foo("cd", "-CD-") %] => ab-CD-
108
109       "++ --"
110           Pre and post increment and decrement.  My be used as either a
111           prefix or postfix operator.
112
113               [% ++a %][% ++a %] => 12
114
115               [% a++ %][% a++ %] => 01
116
117               [% --a %][% --a %] => -1-2
118
119               [% a-- %][% a-- %] => 0-1
120
121       "**  ^  pow"
122           Right associative binary.  X raised to the Y power.  This isn't
123           available in TT 2.15.
124
125               [% 2 ** 3 %] => 8
126
127       "!" Prefix not.  Negation of the value.
128
129       "-" Prefix minus.  Returns the value multiplied by -1.
130
131               [% a = 1 ; b = -a ; b %] => -1
132
133       "*" Left associative binary. Multiplication.
134
135       "/  div  DIV"
136           Left associative binary. Division.  Note that / is floating point
137           division, but div and DIV are integer division.
138
139              [% 10  /  4 %] => 2.5
140              [% 10 div 4 %] => 2
141
142       "%  mod  MOD"
143           Left associative binary. Modulus.
144
145              [% 15 % 8 %] => 7
146
147       "+" Left associative binary.  Addition.
148
149       "-" Left associative binary.  Minus.
150
151       "_  ~"
152           Left associative binary.  String concatenation.
153
154               [% "a" ~ "b" %] => ab
155
156       "<  >  <=  >="
157           Non associative binary.  Numerical comparators.
158
159       "lt  gt  le  ge"
160           Non associative binary.  String comparators.
161
162       "eq"
163           Non associative binary.  String equality test.
164
165       "=="
166           Non associative binary. In TT syntaxes the V2EQUALS configuration
167           item defaults to true which means this operator will operate the
168           same as the "eq" operator.  Setting V2EQUALS to 0 will change this
169           operator to mean numeric equality.  You could also use [% ! (a <=>
170           b) %] but that is a bit messy.
171
172           The HTML::Template syntaxes default V2EQUALS to 0 which means that
173           it will test for numeric equality just as you would normally
174           expect.
175
176           In either case - you should always use "eq" when you mean "eq".
177           The V2EQUALS will most likely eventually default to 0.
178
179       "ne"
180           Non associative binary.  String non-equality test.
181
182       "!="
183           Non associative binary. In TT syntaxes the V2EQUALS configuration
184           item defaults to true which means this operator will operate the
185           same as the "ne" operator.  Setting V2EQUALS to 0 will change this
186           operator to mean numeric non-equality.  You could also use [% (a
187           <=> b) %] but that is a bit messy.
188
189           The HTML::Template syntaxes default V2EQUALS to 0 which means that
190           it will test for numeric non-equality just as you would normally
191           expect.
192
193           In either case - you should always use "ne" when you mean "ne".
194           The V2EQUALS will most likely eventually default to 0.
195
196       "<=>"
197           Non associative binary.  Numeric comparison operator.  Returns -1
198           if the first argument is less than the second, 0 if they are equal,
199           and 1 if the first argument is greater.
200
201       "cmp"
202           Non associative binary.  String comparison operator.  Returns -1 if
203           the first argument is less than the second, 0 if they are equal,
204           and 1 if the first argument is greater.
205
206       "&&"
207           Left associative binary.  And.  All values must be true.  If all
208           values are true, the last value is returned as the truth value.
209
210               [% 2 && 3 && 4 %] => 4
211
212       "||"
213           Right associative binary.  Or.  The first true value is returned.
214
215               [% 0 || '' || 7 %] => 7
216
217           Note: perl is left associative on this operator - but it doesn't
218           matter because || has its own precedence level.  Setting it to
219           right allows for Alloy to short circuit earlier in the expression
220           optree (left is (((1,2), 3), 4) while right is (1, (2, (3, 4))).
221
222       "//"
223           Right associative binary.  Perl 6 err.  The first defined value is
224           returned.
225
226               [% foo // bar %]
227
228       ".."
229           Non associative binary.  Range creator.  Returns an arrayref
230           containing the values between and including the first and last
231           arguments.
232
233               [% t = [1 .. 5] %] => variable t contains an array with 1,2,3,4, and 5
234
235           It is possible to place multiple ranges in the same [] constructor.
236           This is not available in TT.
237
238               [% t = [1..3, 6..8] %] => variable t contains an array with 1,2,3,6,7,8
239
240           The .. operator is the only operator that returns a list of items.
241
242       "? :"
243           Ternary - right associative.  Can be nested with other ?: pairs.
244
245               [% 1 ? 2 : 3 %] => 2
246               [% 0 ? 2 : 3 %] => 3
247
248       "*= += -= /= **= %= ~="
249           Self-modifying assignment - right associative.  Sets the left hand
250           side to the operation of the left hand side and right (clear as
251           mud).  In order to not conflict with SET, FOREACH and other
252           operations, this operator is only available in parenthesis.
253
254              [% a = 2 %][%  a += 3  %] --- [% a %]    => --- 5   # is handled by SET
255              [% a = 2 %][% (a += 3) %] --- [% a %]    => 5 --- 5
256
257       "=" Assignment - right associative.  Sets the left-hand side to the
258           value of the righthand side.  In order to not conflict with SET,
259           FOREACH and other operations, this operator is only available in
260           parenthesis.  Returns the value of the righthand side.
261
262              [%  a = 1  %] --- [% a %]    => --- 1   # is handled by SET
263              [% (a = 1) %] --- [% a %]    => 1 --- 1
264
265       "not  NOT"
266           Prefix. Lower precedence version of the '!' operator.
267
268       "and  AND"
269           Left associative. Lower precedence version of the '&&' operator.
270
271       "or OR"
272           Right associative. Lower precedence version of the '||' operator.
273
274       "err ERR"
275           Right associative.  Lower precedence version of the '//' operator.
276
277       "->" (Not in TT2)
278           Macro operator.  Works like the MACRO directive but can be used in
279           map, sort, and grep list operations.  Syntax is based on the Perl 6
280           pointy sub.  There are two differences from the MACRO directive.
281           First is that if no argument list is specified, a default argument
282           list with a single parameter named "this" will be used.  Second,
283           the "->" operator parses its block as if it was already in a
284           template tag.
285
286               [% foo = ->{ "Hi" } %][% foo %] => Hi
287               [% foo = ->{ this.repeat(2) } %][% foo("Hi") %] => HiHi
288               [% foo = ->(n){ n.repeat(2) } %][% foo("Hi") %] => HiHi
289               [% foo = ->(a,b){ a; "|"; b } %][% foo(2,3) %]  => 2|3
290
291               [% [0..10].grep(->{ this % 2 }).join %] => 1 3 5 7 9
292               [% ['a'..'c'].map(->{ this.upper }).join %] => A B C
293
294               [% [1,2,3].sort(->(a,b){ b <=> a }).join %] prints 3 2 1
295
296               [% c = [{k => "wow"}, {k => "wee"}, {k => "a"}] %]
297               [% c.sort(->(a,b){ a.k cmp b.k }).map(->{this.k}).join %] => a wee wow
298
299           Note: Care should be used when attempting to sort large lists.  The
300           mini-language of Template::Alloy is a interpreted language running
301           in Perl which is an interpreted language.  There are likely to be
302           performance issues when trying to do low level functions such as
303           sort on large lists.
304
305           The RETURN directive and return item, list, and hash vmethods can
306           be used to return more interesting values from a MACRO.
307
308             [% a = ->(n){ [1..n].return } %]
309             [% a(3).join %]    => 1 2 3
310             [% a(10).join %]   => 1 2 3 4 5 6 7 8 9 10
311
312           The Schwartzian transform is now possible in Template::Alloy
313           (somebody somewhere is rolling over in their grave).
314
315             [%- qw(Z a b D y M)
316                   .map(->{ [this.lc, this].return })
317                   .sort(->(a,b){a.0 cmp b.0})
318                   .map(->{this.1})
319                   .join %]          => a b D M y Z
320
321       "{}"
322           This operator is not exposed for external use.  It is used
323           internally by Template::Alloy to delay the creation of a hash until
324           the execution of the compiled template.
325
326       "[]"
327           This operator is not exposed for external use.  It is used
328           internally by Template::Alloy to delay the creation of an array
329           until the execution of the compiled template.
330
331       "@()"
332           List context specifier.  Methods or functions inside this operator
333           will always be called in list context and will always return an
334           arrayref of the results.  See the CALL_CONTEXT configuration
335           directive.
336
337       "$()"
338           Item context specifier.  Methods or functions inside this operator
339           will always be called in item (scalar) context.  See the
340           CALL_CONTEXT configuration directive.
341
342       "qr"
343           This operator is not exposed for external use.  It is used
344           internally by Template::Alloy to store a regular expression and its
345           options.  It will return a compiled Regexp object when compiled.
346
347       "-temp-"
348           This operator is not exposed for external use.  It is used
349           internally by some directives to pass temporary, literal data into
350           play_expr to allow additional vmethods or filters to be called on
351           existing data.
352

AUTHOR

354       Paul Seamons <paul@seamons.com>
355

LICENSE

357       This module may be distributed under the same terms as Perl itself.
358
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361perl v5.34.0                      2021-07-22      Template::Alloy::Operator(3)
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