diff options
Diffstat (limited to 'contrib/gcc/cp/templates.texi')
| -rw-r--r-- | contrib/gcc/cp/templates.texi | 235 |
1 files changed, 0 insertions, 235 deletions
diff --git a/contrib/gcc/cp/templates.texi b/contrib/gcc/cp/templates.texi deleted file mode 100644 index 2a6db07..0000000 --- a/contrib/gcc/cp/templates.texi +++ /dev/null @@ -1,235 +0,0 @@ -@node Templates -@chapter The Template Implementation - -@cindex templates -@cindex function templates -@cindex class templates -@cindex parameterized types -@cindex types, parameterized -The C++ template@footnote{Class templates are also known as -@dfn{parameterized types}.} facility, which effectively allows use of -variables for types in declarations, is one of the newest features of -the language. - -@sc{gnu} C++ is one of the first compilers to implement many -of the template facilities currently defined by the @sc{ansi} committee. - -Nevertheless, the template implementation is not yet complete. This -chapter maps the current limitations of the @sc{gnu} C++ template -implementation. - -@menu -* Template limitations:: Limitations for function and class templates -* Function templates:: Limitations for function templates -* Class templates:: Limitations for class templates -* Template debugging:: Debugging information for templates -@end menu - -@node Template limitations -@section Limitations for function and class templates - -@cindex template limitations -@cindex template bugs -@cindex bugs, templates -These limitations apply to any use of templates (function templates or -class templates) with @sc{gnu} C++: - -@table @emph -@item Template definitions must be visible -When you compile code with templates, the template definitions must come -first (before the compiler needs to expand them), and template -definitions you use must be visible in the current scope. -@c FIXME! Is this a defined property of templates, rather than a -@c temporary limitation? -@c ANSWER: It's a limitation, but it's hard to say why it's a limitation -@c to someone. We need an infinite link-cycle, in one camp, to -@c accomplish things so you don't need the template definitions around. - -@cindex static data in template classes -@cindex template classes, static data in -@item Individual initializers needed for static data -Templates for static data in template classes do not work. @xref{Class -templates,,Limitations for class templates}. -@end table - -@node Function templates -@section Limitations for function templates - -@cindex function template limitations -Function templates are implemented for the most part. The compiler can -correctly determine template parameter values, and will delay -instantiation of a function that uses templates until the requisite type -information is available. - -@noindent -The following limitations remain: - -@itemize @bullet -@cindex template vs declaration, functions -@cindex declaration vs template, functions -@cindex function declaration vs template -@item -Narrowed specification: function declarations should not prevent -template expansion. When you declare a function, @sc{gnu} C++ -interprets the declaration as an indication that you will provide a -definition for that function. Therefore, @sc{gnu} C++ does not use a -template expansion if there is also an applicable declaration. @sc{gnu} -C++ only expands the template when there is no such declaration. - -The specification in Bjarne Stroustrup's @cite{The C++ Programming -Language, Second Edition} is narrower, and the @sc{gnu} C++ -implementation is now clearly incorrect. With this new specification, a -declaration that corresponds to an instantiation of a function template -only affects whether conversions are needed to use that version of the -function. It should no longer prevent expansion of the template -definition. - -For example, this code fragment must be treated differently: - -@smallexample -template <class X> X min (X& x1, X& x2) @{ @dots{} @} -int min (int, int); -@dots{} -int i; short s; -min (i, s); // @r{should call} min(int,int) - // @r{derived from template} -@dots{} -@end smallexample - -@item -The compiler does not yet understand function signatures where types are -nested within template parameters. For example, a function like the -following produces a syntax error on the closing @samp{)} of the -definition of the function @code{f}: - -@smallexample -template <class T> class A @{ public: T x; class Y @{@}; @}; -template <class X> int f (A<X>::Y y) @{ @dots{} @} -@end smallexample - -@cindex @code{inline} and function templates -@cindex function templates and @code{inline} -@item -If you declare an @code{inline} function using templates, the compiler -can only inline the code @emph{after} the first time you use -that function with whatever particular type signature the template -was instantiated. - -Removing this limitation is akin to supporting nested function -definitions in @sc{gnu} C++; the limitation will probably remain until the -more general problem of nested functions is solved. - -@item -All the @emph{method} templates (templates for member functions) for a -class must be visible to the compiler when the class template is -instantiated. -@end itemize - -@node Class templates -@section Limitations for class templates - -@cindex class template limitations -@ignore -FIXME!! Include a comprehensible version of this if someone can explain it. - (Queried Brendan and Raeburn w/full orig context, 26may1993---pesch) - - [RHP: I don't understand what the following fragment refers to. If it's - the "BIG BUG" section in the original, why does it say "overriding class - declarations" here when the more detailed text refers to *function* - declarations? Here's the fragment I don't understand:] - there are problems with user-supplied overriding class declarations (see - below). -@end ignore - -@itemize @bullet -@ignore -@cindex static data, not working in templates -@item -Templates for static data in template classes do not work. -Currently, you must initialize each case of such data -individually. -@c FIXME!! Brendan to see if still true. -@c ANSWER: This section presumes that it's incorrect to have to -@c initialize for each type you instantiate with. It's not, it's the -@c right way to do it. -@end ignore - -Unfortunately, individual initializations of this sort are likely to be -considered errors eventually; since they're needed now, you might want to -flag places where you use them with comments to mark the need for a -future transition. - -@cindex nested type results vs templates -@item -Member functions in template classes may not have results of nested -type; @sc{gnu} C++ signals a syntax error on the attempt. The following -example illustrates this problem with an @code{enum} type @code{alph}: - -@smallexample -template <class T> class list @{ - @dots{} - enum alph @{a,b,c@}; - alph bar(); - @dots{} -@}; - -template <class T> -list<int>::alph list<int>::bar() // @i{Syntax error here} -@{ -@dots{} -@} -@end smallexample - -@cindex preprocessor conditionals in templates -@cindex conditionals (preprocessor) in templates -@item -A parsing bug makes it difficult to use preprocessor conditionals within -templates. For example, in this code: - -@smallexample -template <class T> -class list @{ - @dots{} -#ifdef SYSWRONG - T x; -#endif - @dots{} -@} -@end smallexample - -The preprocessor output leaves sourcefile line number information (lines -like @samp{# 6 "foo.cc"} when it expands the @code{#ifdef} block. These -lines confuse the compiler while parsing templates, giving a syntax -error. - -If you cannot avoid preprocessor conditionals in templates, you can -suppress the line number information using the @samp{-P} preprocessor -option (but this will make debugging more difficult), by compiling the -affected modules like this: - -@smallexample -g++ -P foo.cc -o foo -@end smallexample - -@cindex parsing errors, templates -@item -Parsing errors are reported when templates are first -@emph{instantiated}---not on the template definition itself. In -particular, if you do not instantiate a template definition at all, the -compiler never reports any parsing errors that may be in the template -definition. -@end itemize - -@node Template debugging -@section Debugging information for templates - -@cindex templates and debugging information -@cindex debugging information and templates -Debugging information for templates works for some object code formats, -but not others. It works for stabs@footnote{Except that insufficient -debugging information for methods of template classes is generated in -stabs.} (used primarily in @sc{a.out} object code, but also in the Solaris 2 -version of @sc{elf}), and the @sc{mips} version of @sc{coff} debugging -format. - -@sc{dwarf} support is currently minimal, and requires further -development. |
