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Diffstat (limited to 'contrib/gcc/doc/objc.texi')
| -rw-r--r-- | contrib/gcc/doc/objc.texi | 40 |
1 files changed, 28 insertions, 12 deletions
diff --git a/contrib/gcc/doc/objc.texi b/contrib/gcc/doc/objc.texi index d3fd775e2c0c..a0c40f7296e6 100644 --- a/contrib/gcc/doc/objc.texi +++ b/contrib/gcc/doc/objc.texi @@ -25,7 +25,6 @@ comments about this document to Ovidiu Predescu @node Executing code before main, Type encoding, Objective-C, Objective-C @section @code{+load}: Executing code before main - The GNU Objective-C runtime provides a way that allows you to execute code before the execution of the program enters the @code{main} function. The code is executed on a per-class and a per-category basis, @@ -396,7 +395,7 @@ prefixing a C constant string with the character @samp{@@}: id myString = @@"this is a constant string object"; @end example -The constant string objects are usually instances of the +The constant string objects are by default instances of the @code{NXConstantString} class which is provided by the GNU Objective-C runtime. To get the definition of this class you must include the @file{objc/NXConstStr.h} header file. @@ -409,8 +408,9 @@ as @code{NXConstantString}'s structure: @example -@@interface NXConstantString : Object +@@interface MyConstantStringClass @{ + Class isa; char *c_string; unsigned int len; @} @@ -418,15 +418,31 @@ as @code{NXConstantString}'s structure: @end example -User class libraries may choose to inherit the customized constant -string class from a different class than @code{Object}. There is no -requirement in the methods the constant string class has to implement. - -When a file is compiled with the @option{-fconstant-string-class} option, -all the constant string objects will be instances of the class specified -as argument to this option. It is possible to have multiple compilation -units referring to different constant string classes, neither the -compiler nor the linker impose any restrictions in doing this. +@code{NXConstantString} inherits from @code{Object}; user class +libraries may choose to inherit the customized constant string class +from a different class than @code{Object}. There is no requirement in +the methods the constant string class has to implement, but the final +ivar layout of the class must be the compatible with the given +structure. + +When the compiler creates the statically allocated constant string +object, the @code{c_string} field will be filled by the compiler with +the string; the @code{length} field will be filled by the compiler with +the string length; the @code{isa} pointer will be filled with +@code{NULL} by the compiler, and it will later be fixed up automatically +at runtime by the GNU Objective-C runtime library to point to the class +which was set by the @option{-fconstant-string-class} option when the +object file is loaded (if you wonder how it works behind the scenes, the +name of the class to use, and the list of static objects to fixup, are +stored by the compiler in the object file in a place where the GNU +runtime library will find them at runtime). + +As a result, when a file is compiled with the +@option{-fconstant-string-class} option, all the constant string objects +will be instances of the class specified as argument to this option. It +is possible to have multiple compilation units referring to different +constant string classes, neither the compiler nor the linker impose any +restrictions in doing this. @c ========================================================================= @node compatibility_alias |