1ExtUtils::Constant::BaseP(e3rplm)Programmers ReferenceEGxutiUdteils::Constant::Base(3pm)
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6 ExtUtils::Constant::Base - base class for ExtUtils::Constant objects
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9 require ExtUtils::Constant::Base;
10 @ISA = 'ExtUtils::Constant::Base';
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13 ExtUtils::Constant::Base provides a base implementation of methods to
14 generate C code to give fast constant value lookup by named string.
15 Currently it's mostly used ExtUtils::Constant::XS, which generates the
16 lookup code for the constant() subroutine found in many XS modules.
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19 ExtUtils::Constant::Base exports no subroutines. The following methods
20 are available
21 header
23 A method returning a scalar containing definitions needed, typi‐
24 cally for a C header file.
25 memEQ_clause args_hashref
27 A method to return a suitable C "if" statement to check whether
28 name is equal to the C variable "name". If checked_at is defined,
29 then it is used to avoid "memEQ" for short names, or to generate a
30 comment to highlight the position of the character in the "switch"
31 statement.
32 If i<checked_at> is a reference to a scalar, then instead it gives
34 the characters pre-checked at the beginning, (and the number of
35 chars by which the C variable name has been advanced. These need to
36 be chopped from the front of name).
37 dump_names arg_hashref, ITEM...
39 An internal function to generate the embedded perl code that will
40 regenerate the constant subroutines. default_type, types and ITEMs
41 are the same as for C_constant. indent is treated as number of
42 spaces to indent by. If "declare_types" is true a $types is always
43 declared in the perl code generated, if defined and false never
44 declared, and if undefined $types is only declared if the values in
45 types as passed in cannot be inferred from default_types and the
46 ITEMs.
47 assign arg_hashref, VALUE...
49 A method to return a suitable assignment clause. If type is aggre‐
50 gate (eg PVN expects both pointer and length) then there should be
51 multiple VALUEs for the components. pre and post if defined give
52 snippets of C code to proceed and follow the assignment. pre will
53 be at the start of a block, so variables may be defined in it.
54 return_clause arg_hashref, ITEM
56 A method to return a suitable "#ifdef" clause. ITEM is a hashref
57 (as passed to "C_constant" and "match_clause". indent is the number
58 of spaces to indent, defaulting to 6.
59 switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM...
61 An internal method to generate a suitable "switch" clause, called
62 by "C_constant" ITEMs are in the hash ref format as given in the
63 description of "C_constant", and must all have the names of the
64 same length, given by NAMELEN. ITEMHASH is a reference to a hash,
65 keyed by name, values being the hashrefs in the ITEM list. (No
66 parameters are modified, and there can be keys in the ITEMHASH that
67 are not in the list of ITEMs without causing problems - the hash is
68 passed in to save generating it afresh for each call).
69 params WHAT
71 An "internal" method, subject to change, currently called to allow
72 an overriding class to cache information that will then be passed
73 into all the "*param*" calls. (Yes, having to read the source to
74 make sense of this is considered a known bug). WHAT is be a hashref
75 of types the constant function will return. In ExtUtils::Con‐
76 stant::XS this method is used to returns a hashref keyed IV NV PV
77 SV to show which combination of pointers will be needed in the C
78 argument list generated by C_constant_other_params_definition and
79 C_constant_other_params
80 dogfood arg_hashref, ITEM...
82 An internal function to generate the embedded perl code that will
83 regenerate the constant subroutines. Parameters are the same as
84 for C_constant.
85 Currently the base class does nothing and returns an empty string.
87 C_constant arg_hashref, ITEM...
89 A function that returns a list of C subroutine definitions that
90 return the value and type of constants when passed the name by the
91 XS wrapper. ITEM... gives a list of constant names. Each can
92 either be a string, which is taken as a C macro name, or a refer‐
93 ence to a hash with the following keys
94 name The name of the constant, as seen by the perl code.
96 type The type of the constant (IV, NV etc)
98 value A C expression for the value of the constant, or a list of
100 C expressions if the type is aggregate. This defaults to
101 the name if not given.
102 macro The C pre-processor macro to use in the "#ifdef". This
104 defaults to the name, and is mainly used if value is an
105 "enum". If a reference an array is passed then the first
106 element is used in place of the "#ifdef" line, and the sec‐
107 ond element in place of the "#endif". This allows pre-pro‐
108 cessor constructions such as
109 #if defined (foo)
111 #if !defined (bar)
112 ...
113 #endif
114 #endif
115 to be used to determine if a constant is to be defined.
117 A "macro" 1 signals that the constant is always defined, so
119 the "#if"/"#endif" test is omitted.
120 default Default value to use (instead of "croak"ing with "your ven‐
122 dor has not defined...") to return if the macro isn't
123 defined. Specify a reference to an array with type followed
124 by value(s).
125 pre C code to use before the assignment of the value of the
127 constant. This allows you to use temporary variables to
128 extract a value from part of a "struct" and return this as
129 value. This C code is places at the start of a block, so
130 you can declare variables in it.
131 post C code to place between the assignment of value (to a tem‐
133 porary) and the return from the function. This allows you
134 to clear up anything in pre. Rarely needed.
135 def_pre
137 def_post
138 Equivalents of pre and post for the default value.
139 utf8 Generated internally. Is zero or undefined if name is 7 bit
141 ASCII, "no" if the name is 8 bit (and so should only match
142 if SvUTF8() is false), "yes" if the name is utf8 encoded.
143 The internals automatically clone any name with characters
145 128-255 but none 256+ (ie one that could be either in bytes
146 or utf8) into a second entry which is utf8 encoded.
147 weight Optional sorting weight for names, to determine the order
149 of linear testing when multiple names fall in the same case
150 of a switch clause. Higher comes earlier, undefined
151 defaults to zero.
152 In the argument hashref, package is the name of the package, and is
154 only used in comments inside the generated C code. subname defaults
155 to "constant" if undefined.
156 default_type is the type returned by "ITEM"s that don't specify
158 their type. It defaults to the value of "default_type()". types
159 should be given either as a comma separated list of types that the
160 C subroutine subname will generate or as a reference to a hash.
161 default_type will be added to the list if not present, as will any
162 types given in the list of ITEMs. The resultant list should be the
163 same list of types that "XS_constant" is given. [Otherwise "XS_con‐
164 stant" and "C_constant" may differ in the number of parameters to
165 the constant function. indent is currently unused and ignored. In
166 future it may be used to pass in information used to change the C
167 indentation style used.] The best way to maintain consistency is
168 to pass in a hash reference and let this function update it.
169 breakout governs when child functions of subname are generated. If
171 there are breakout or more ITEMs with the same length of name, then
172 the code to switch between them is placed into a function named
173 subname_len, for example "constant_5" for names 5 characters long.
174 The default breakout is 3. A single "ITEM" is always inlined.
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177 Not everything is documented yet.
178 Probably others.
180
182 Nicholas Clark <nick@ccl4.org> based on the code in "h2xs" by Larry
183 Wall and others
184perl v5.8.8 2001-09-21 ExtUtils::Constant::Base(3pm)