The source code for Tcl is managed by fossil. Tcl developers coordinate all
changes to the Tcl source code at
> [Tcl Source Code](https://core.tcl-lang.org/tcl/timeline)
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
- <code>0<i>NNN</i></code> format is no longer octal interpretation. Use <code>0o<i>NNN</i></code>.
- <code>0d<i>NNNN</i></code> format to compel decimal interpretation.
- <code>NN_NNN_NNN</code>, 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`
# Known bugs
- [Command line built with list not properly quoted](https://core.tcl-lang.org/tcl/tktview/e38dce)
- [changed behaviour wrt command names, namespaces and resolution](https://core.tcl-lang.org/tcl/tktview/f14b33)
- [classmethod fails if no argument supplied to class create](https://core.tcl-lang.org/tcl/tktview/680503)
- [windows dos device paths inconsistencies and missing functionality](https://core.tcl-lang.org/tcl/tktview/d8f121)
- [zlib-8.8, zlib-8.16 fail on Fedora 40, gcc 14.1.1](https://core.tcl-lang.org/tcl/tktview/73d5cb)
- [Temporary folder with file "tcl9registry13.dll" remains after "exit"](https://core.tcl-lang.org/tcl/tktview/6ce3c0)
