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Tcl Source Code

Release Tcl 9.0.0 arises from the check-in with tag core-9-0-0.

Highlighted differences between Tcl 9.0 and Tcl 8.6 are summarized below, with focus on changes important to programmers using the Tcl library and writing Tcl scripts.

Major Features

64-bit capacity: Data values larger than 2Gb

Strings can be any length (that fits in your available memory)
Lists and dictionaries can have very large numbers of elements

Internationalization of text

Full Unicode range of codepoints
New encodings: utf-16/utf-32/ucs-2(le|be), CESU-8, etc.
encoding options -profile, -failindex manage encoding of I/O.
msgcat supports custom locale search list
source defaults to -encoding utf-8

Zip filesystems and attached archives.

Packaging of the Tcl script library with the Tcl binary library, meaning that the TCL_LIBRARY environment variable is usually not required.
Packaging of an application into a virtual filesystem is now a supported core Tcl feature.

Unix notifiers available using `epoll()` or `kqueue()`

This relieves limits on file descriptors imposed by legacy select() and fixes a performance bottleneck.

Incompatibilities

Notable incompatibilities

Unqualified varnames resolved in current namespace, not global. Note that in almost all cases where this causes a change, the change is actually the removal of a latent bug.
No --disable-threads build option. Always thread-enabled.
I/O malencoding default response: raise error (-profile strict)
Windows platform needs Windows 7 or Windows Server 2008 R2 or later
Ended interpretation of ~ as home directory in pathnames. (See file home and file tildeexpand for replacements when you need them.)
Removed the identity encoding. (There were only ever very few valid use cases for this; almost all uses were systematically wrong.)
Removed the encoding alias binary to iso8859-1.
$::tcl_precision no longer controls string generation of doubles. (If you need a particular precision, use format.)
Removed pre-Tcl 8 legacies: case, puts and read variant syntaxes.
Removed subcommands [trace variable|vdelete|vinfo]
No -eofchar option for channels anymore for writing.
On Windows 10+ (Version 1903 or higher), system encoding is always utf-8.
%b/%d/%o/%x format modifiers (without size modifier) for format and scan always truncate to 32-bits on all platforms.
%L size modifier for scan no longer truncates to 64-bit.
Removed command ::tcl::unsupported::inject. (See coroinject and coroprobe for supported commands with significantly more comprehensible semantics.)

Incompatibilities in C public interface

Many arguments expanded type from int to Tcl_Size, a signed integer type large enough to support 64-bit sized memory objects. The constant TCL_AUTO_LENGTH is a value of that type that indicates that the length should be obtained using an appropriate function (typically strlen() for char * values).
Ended support for Tcl_ChannelTypeVersion less than 5
Introduced versioning of the Tcl_ObjType struct
Removed macros CONST*: Tcl 9 support means dropping Tcl 8.3 support. (Replaced with standard C const keyword going forward.)
Removed routines:

Tcl_Backslash(), Tcl_*VA(), Tcl_*MathFunc*(), Tcl_MakeSafe(), Tcl_(Save|Restore|Discard|Free)Result(), Tcl_EvalTokens(), Tcl_(Get|Set)DefaultEncodingDir(), Tcl_UniCharN(case)cmp(), Tcl_UniCharCaseMatch()

Note that builds of extensions against Tcl 8.6 and before are expected to not work with Tcl 9.0; ABI compatibility was a non-goal for 9.0. In most cases, rebuilding the code against Tcl 9.0 should work except when a removed API function is used.

New Features

New commands

array default — Specify default values for arrays (note that this alters the behaviour of append, incr, lappend).
array for — Cheap iteration over an array's contents.
chan isbinary — Test if a channel is configured to work with binary data.
coroinject, coroprobe — Interact with paused coroutines.
clock add weekdays — Clock arithmetic with week days.
const, info const* — Commands for defining constants (variables that can't be modified).
dict getwithdefault — Define a fallback value to use when dict get would otherwise fail.
file home — Get the user home directory.
file tempdir — Create a temporary directory.
file tildeexpand — Expand a file path containing a ~.
info commandtype — Introspection for the kinds of commands.
ledit — Equivalent to lreplace but on a list in a variable.
lpop — Remove an item from a list in a variable.
lremove — Remove a sublist from a list in a variable.
lseq — Generate a list of numbers in a sequence.
package files — Describe the contents of a package.
string insert — Insert a string as a substring of another string.
string is dict — Test whether a string is a dictionary.
tcl::process — Commands for working with subprocesses.
*::build-info — Obtain information about the build of Tcl.
readFile, writeFile, foreachLine — Simple procedures for basic working with files.
tcl::idna::* — Commands for working with encoded DNS names.

New command options

chan configure ... -inputmode ... — Support for raw terminal input and reading passwords.
clock scan ... -validate ...
info loaded ... ?prefix?
lsearch ... -stride ... — Search a list by groups of items.
regsub ... -command ... — Generate the replacement for a regular expression by calling a command.
socket ... -nodelay ... -keepalive ...
vwait controlled by several new options
expr string comparators lt, gt, le, ge
expr supports comments inside expressions

Numbers

0NNN format is no longer octal interpretation. Use 0oNNN.
0dNNNN format to compel decimal interpretation.
NN_NNN_NNN, underscores in numbers for optional readability
Functions: isinf(), isnan(), isnormal(), issubnormal(), isunordered()
Command: fpclassify
Function int() no longer truncates to word size

TclOO facilities

private variables and methods
class variables and methods
abstract and singleton classes
configurable properties
method -export, method -unexport