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Updated doc doe BOOST_PP_OVERLOAD.

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Edward Diener
2020-07-03 14:18:44 -04:00
parent e231fe7ad9
commit 5c7ae49828
2 changed files with 56 additions and 48 deletions
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34
doc/topics/variadic_macros.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html; charset=windows-1252"
@ -141,8 +141,8 @@
<div> In the C++20 specification there is a new construct which can
be used in the expansion of a variadic macro, called __VA_OPT__.
This construct when used in the expansion of a variadic macro is
followed by an opening paranthesis ('('), preprocessor data, and a
closing parenthesis ('}'). When the variadic data passed by the
followed by an opening paranthesis '(', preprocessor data, and a
closing parenthesis ')'. When the variadic data passed by the
invocation of a variadic macro is empty, this new construct
expands to nothing. When the variadic data passed by the
invocation of a variadic macro is not empty, this new construct
@ -159,21 +159,23 @@
it returns 0. <br>
<br>
When the __VA_OPT__ construct is supported in C++20 mode the
variadic data passed to the variadic macros can be empty,
otherwise when not in this mode variadic data passed to the
variadic macros should never be empty. In this C+++20 mode
invoking BOOST_PP_VARIADIC_SIZE with empty data expands to 0,
invoking BOOST_PP_VARIADIC_TO_ARRAY with empty data expands to the
empty array '(0,())', and invoking BOOST_PP_VARIADIC_TO_LIST with
empty data expands to the empty list 'BOOST_PP_NIL'. Similarly in
this C++20 mode passing an empty array '(0,())' to
BOOST_PP_ARRAY_ENUM expands to empty variadic data and passing an
empty list 'BOOST_PP_NIL' to BOOST_PP_LIST_ENUM also expands to
empty variadic data. Neither a seq or a tuple can be empty so
passing empty variadic data to either BOOST_PP_VARIADIC_TO_SEQ or
variadic data passed to the variadic macros and to
BOOST_PP_OVERLOAD can be empty, otherwise when not in this mode
variadic data passed to the variadic macros should never be empty.
In this C+++20 mode invoking BOOST_PP_VARIADIC_SIZE with empty
data expands to 0, invoking BOOST_PP_VARIADIC_TO_ARRAY with empty
data expands to the empty array '(0,())', invoking
BOOST_PP_VARIADIC_TO_LIST with empty data expands to the empty
list 'BOOST_PP_NIL', and invoking BOOST_PP_OVERLOAD with empty
data creates an overload name with 0 appended. Similarly in this
C++20 mode passing an empty array '(0,())' to BOOST_PP_ARRAY_ENUM
expands to empty variadic data and passing an empty list
'BOOST_PP_NIL' to BOOST_PP_LIST_ENUM also expands to empty
variadic data. Neither a seq or a tuple can be empty so passing
empty variadic data to either BOOST_PP_VARIADIC_TO_SEQ or
BOOST_PP_VARIADIC_TO_TUPLE is erroneous. Likewise passing empty
data to BOOST_PP_VARIADIC_ELEM is always erroneous since there are
no tokens of variadic data to access. <br>
no tokens of variadic data to access.<br>
</div>
<u style="font-weight: bold;"> Using a Tuple Instead of an Array<br>
</u>