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* extend.texi (Bound member functions): Document.

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From-SVN: r24483
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Jason Merrill 1999-01-04 11:56:18 +00:00 committed by Jason Merrill
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gcc/ChangeLog
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@ -1,3 +1,7 @@
Mon Jan 4 11:55:51 1999 Jason Merrill <jason@yorick.cygnus.com>
* extend.texi (Bound member functions): Document.
Mon Jan 4 11:01:48 1999 Kaveh R. Ghazi <ghazi@caip.rutgers.edu>
* mips-tdump.c (st_to_string, sc_to_string, glevel_to_string,

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gcc/extend.texi
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@c Copyright (C) 1988,89,92,93,94,96 Free Software Foundation, Inc.
@c Copyright (C) 1988,89,92,93,94,96,99 Free Software Foundation, Inc.
@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.
@ -3015,8 +3015,11 @@ Predefined Macros,cpp.info,The C Preprocessor}).
declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
method denoted by a @samp{->*} or @samp{.*} expression.
* C++ Signatures:: You can specify abstract types to get subtype
polymorphism independent from inheritance.
@end menu
@node Naming Results
@ -3476,6 +3479,40 @@ be the same in all translation units, or things are likely to break.
more discussion of these pragmas.
@end enumerate
@node Bound member functions
@section Extracting the function pointer from a bound pointer to member function
@cindex pmf
@cindex pointer to member function
@cindex bound pointer to member function
In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the @samp{this} pointer,
and if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function. If you are using
PMFs in an inner loop, you should really reconsider that decision. If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.
Note that you will still be paying the penalty for the call through a
function pointer; on most modern architectures, such a call defeats the
branch prediction features of the CPU. This is also true of normal
virtual function calls.
The syntax for this extension is
@example
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);
fptr p = (fptr)(a.*fp);
@end example
You must specify @samp{-Wno-pmf-conversions} to use this extension.
@node C++ Signatures
@section Type Abstraction using Signatures