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pkg_mkIndex(n) Tcl Built-In Commands pkg_mkIndex(n)
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NAME
pkg_mkIndex - Build an index for automatic loading of packages
SYNOPSIS
pkg_mkIndex ?-direct? ?-lazy? ?-load pkgPat? ?-verbose? dir ?pattern pattern ...?
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DESCRIPTION
Pkg_mkIndex is a utility procedure that is part of the standard Tcl library. It is used
to create index files that allow packages to be loaded automatically when package require
commands are executed. To use pkg_mkIndex, follow these steps:
[1] Create the package(s). Each package may consist of one or more Tcl script files or
binary files. Binary files must be suitable for loading with the load command with
a single argument; for example, if the file is test.so it must be possible to load
this file with the command load test.so. Each script file must contain a package
provide command to declare the package and version number, and each binary file
must contain a call to Tcl_PkgProvide.
[2] Create the index by invoking pkg_mkIndex. The dir argument gives the name of a
directory and each pattern argument is a glob-style pattern that selects script or
binary files in dir. The default pattern is *.tcl and *.[info sharedlibextension].
Pkg_mkIndex will create a file pkgIndex.tcl in dir with package information about
all the files given by the pattern arguments. It does this by loading each file
into a slave interpreter and seeing what packages and new commands appear (this is
why it is essential to have package provide commands or Tcl_PkgProvide calls in the
files, as described above). If you have a package split among scripts and binary
files, or if you have dependencies among files, you may have to use the -load
option or adjust the order in which pkg_mkIndex processes the files. See COMPLEX
CASES below.
[3] Install the package as a subdirectory of one of the directories given by the
tcl_pkgPath variable. If $tcl_pkgPath contains more than one directory, machine-
dependent packages (e.g., those that contain binary shared libraries) should nor-
mally be installed under the first directory and machine-independent packages
(e.g., those that contain only Tcl scripts) should be installed under the second
directory. The subdirectory should include the package's script and/or binary
files as well as the pkgIndex.tcl file. As long as the package is installed as a
subdirectory of a directory in $tcl_pkgPath it will automatically be found during
package require commands.
If you install the package anywhere else, then you must ensure that the directory
containing the package is in the auto_path global variable or an immediate subdi-
rectory of one of the directories in auto_path. Auto_path contains a list of
directories that are searched by both the auto-loader and the package loader; by
default it includes $tcl_pkgPath. The package loader also checks all of the subdi-
rectories of the directories in auto_path. You can add a directory to auto_path
explicitly in your application, or you can add the directory to your TCLLIBPATH
environment variable: if this environment variable is present, Tcl initializes
auto_path from it during application startup.
[4] Once the above steps have been taken, all you need to do to use a package is to
invoke package require. For example, if versions 2.1, 2.3, and 3.1 of package Test
have been indexed by pkg_mkIndex, the command package require Test will make ver-
sion 3.1 available and the command package require -exact Test 2.1 will make ver-
sion 2.1 available. There may be many versions of a package in the various index
files in auto_path, but only one will actually be loaded in a given interpreter,
based on the first call to package require. Different versions of a package may be
loaded in different interpreters.
OPTIONS
The optional switches are:
-direct The generated index will implement direct loading of the package upon pack-
age require. This is the default.
-lazy The generated index will manage to delay loading the package until the use
of one of the commands provided by the package, instead of loading it imme-
diately upon package require. This is not compatible with the use of
auto_reset, and therefore its use is discouraged.
-load pkgPat The index process will pre-load any packages that exist in the current
interpreter and match pkgPat into the slave interpreter used to generate
the index. The pattern match uses string match rules, but without making
case distinctions. See COMPLEX CASES below.
-verbose Generate output during the indexing process. Output is via the tclLog pro-
cedure, which by default prints to stderr.
-- End of the flags, in case dir begins with a dash.
PACKAGES AND THE AUTO-LOADER
The package management facilities overlap somewhat with the auto-loader, in that both
arrange for files to be loaded on-demand. However, package management is a higher-level
mechanism that uses the auto-loader for the last step in the loading process. It is gen-
erally better to index a package with pkg_mkIndex rather than auto_mkindex because the
package mechanism provides version control: several versions of a package can be made
available in the index files, with different applications using different versions based
on package require commands. In contrast, auto_mkindex does not understand versions so it
can only handle a single version of each package. It is probably not a good idea to index
a given package with both pkg_mkIndex and auto_mkindex. If you use pkg_mkIndex to index a
package, its commands cannot be invoked until package require has been used to select a
version; in contrast, packages indexed with auto_mkindex can be used immediately since
there is no version control.
HOW IT WORKS
Pkg_mkIndex depends on the package unknown command, the package ifneeded command, and the
auto-loader. The first time a package require command is invoked, the package unknown
script is invoked. This is set by Tcl initialization to a script that evaluates all of
the pkgIndex.tcl files in the auto_path. The pkgIndex.tcl files contain package ifneeded
commands for each version of each available package; these commands invoke package pro-
vide commands to announce the availability of the package, and they setup auto-loader
information to load the files of the package. If the -lazy flag was provided when the
pkgIndex.tcl was generated, a given file of a given version of a given package is not
actually loaded until the first time one of its commands is invoked. Thus, after invoking
package require you may not see the package's commands in the interpreter, but you will be
able to invoke the commands and they will be auto-loaded.
DIRECT LOADING
Some packages, for instance packages which use namespaces and export commands or those
which require special initialization, might select that their package files be loaded
immediately upon package require instead of delaying the actual loading to the first use
of one of the package's command. This is the default mode when generating the package
index. It can be overridden by specifying the -lazy argument.
COMPLEX CASES
Most complex cases of dependencies among scripts and binary files, and packages being
split among scripts and binary files are handled OK. However, you may have to adjust the
order in which files are processed by pkg_mkIndex. These issues are described in detail
below.
If each script or file contains one package, and packages are only contained in one file,
then things are easy. You simply specify all files to be indexed in any order with some
glob patterns.
In general, it is OK for scripts to have dependencies on other packages. If scripts con-
tain package require commands, these are stubbed out in the interpreter used to process
the scripts, so these do not cause problems. If scripts call into other packages in
global code, these calls are handled by a stub unknown command. However, if scripts make
variable references to other package's variables in global code, these will cause errors.
That is also bad coding style.
If binary files have dependencies on other packages, things can become tricky because it
is not possible to stub out C-level APIs such as Tcl_PkgRequire API when loading a binary
file. For example, suppose the BLT package requires Tk, and expresses this with a call to
Tcl_PkgRequire in its Blt_Init routine. To support this, you must run pkg_mkIndex in an
interpreter that has Tk loaded. You can achieve this with the -load pkgPat option. If
you specify this option, pkg_mkIndex will load any packages listed by info loaded and that
match pkgPat into the interpreter used to process files. In most cases this will satisfy
the Tcl_PkgRequire calls made by binary files.
If you are indexing two binary files and one depends on the other, you should specify the
one that has dependencies last. This way the one without dependencies will get loaded and
indexed, and then the package it provides will be available when the second file is pro-
cessed. You may also need to load the first package into the temporary interpreter used
to create the index by using the -load flag; it will not hurt to specify package patterns
that are not yet loaded.
If you have a package that is split across scripts and a binary file, then you should
avoid the -load flag. The problem is that if you load a package before computing the index
it masks any other files that provide part of the same package. If you must use -load,
then you must specify the scripts first; otherwise the package loaded from the binary file
may mask the package defined by the scripts.
SEE ALSO
package(n)
KEYWORDS
auto-load, index, package, version
Tcl 8.3 pkg_mkIndex(n)
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