ns-hooks                package:base                R Documentation

_H_o_o_k_s _f_o_r _N_a_m_e _S_p_a_c_e _e_v_e_n_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     Packages with name spaces can supply functions to be called when
     loaded, attached or unloaded.

_U_s_a_g_e:

     .onLoad(libname, pkgname)
     .onAttach(libname, pkgname)
     .onUnload(libpath)

_A_r_g_u_m_e_n_t_s:

 libname: a character string giving the library directory where the
          package defining the namespace was found.

 pkgname: a character string giving the name of the name space.

 libpath: a character string giving the complete path to the package.

_D_e_t_a_i_l_s:

     These functions apply only to packages with name spaces.

     After loading, 'loadNamespace' looks for a hook function named
     '.onLoad' and runs it before sealing the namespace and processing
     exports.

     If a name space is unloaded (via 'unloadNamespace'), a hook
     function '.onUnload' is run before final unloading.

     Note that the code in '.onLoad' and '.onUnload' is run without the
     package being on the search path, but (unless circumvented)
     lexical scope will make objects in the namespace and its imports
     visible. (Do not use the double colon operator in '.onLoad' as
     exports have not been processed at the point it is run.)

     When the package is attached (via 'library'), the hook function
     '.onAttach' is called after the exported functions are attached. 
     This is less likely to be useful than '.onLoad', which should be
     seen as the analogue of '.First.lib' (which is only used for
     packages without a name space).

     '.onLoad', '.onUnload' and '.onAttach' are looked for as internal
     variables in the name space and should not be exported.

     If a function '.Last.lib' is visible in the package, it will be
     called when the package is detached: this does need to be
     exported.

     Anything needed for the functioning of the name space should be
     handled at load/unload times by the '.onLoad' and '.onUnload'
     hooks.  For example, shared libraries can be loaded (unless done
     by a 'useDynib' directive in the 'NAMESPACE' file) and initialized
     in '.onLoad' and unloaded in '.onUnload'.  Use '.onAttach' only
     for actions that are needed only when the package becomes visible
     to the user, for example a start-up message.

_S_e_e _A_l_s_o:

     'setHook' shows how users can set hooks on the same events.

