(in-package :sb-manual) (defsection @deprecation (:title "Deprecation" :concepts ("deprecation")) "In order to support evolution of interfaces in SBCL as well as in user code, SBCL allows declaring functions, variables and types as deprecated. Users of deprecated things are notified by means of warnings while the deprecated thing in question is still available. This chapter documents the interfaces for being notified when using deprecated thing and declaring things as deprecated, the deprecation process used for SBCL interfaces, and lists legacy interfaces in various stages of deprecation. _Deprecation_ in this context should not be confused with those things the ANSI Common Lisp standard calls _deprecated_: the entirety of ANSI CL is supported by SBCL, and none of those interfaces are subject to censure." (@why-deprecate? section) (@the-deprecation-pipeline section) (@deprecation-conditions section) (@introspecting-deprecation-information section) (@deprecation-declaration section) (@deprecation-examples section) (@deprecated-interfaces-in-sbcl section)) (defsection @why-deprecate? (:title "Why Deprecate?") "While generally speaking we try to keep SBCL changes as backwards compatible as feasible, there are situations when existing interfaces are deprecated: - __Broken Interfaces__ Sometimes it turns out that an interface is sufficiently misdesigned that fixing it would be worse than deprecating it and replacing it with another. This is typically the case when fixing the interface would change its semantics in ways that could break user code subtly: in such cases we may end up considering the obvious breakage caused by deprecation to be preferable. Another example are functions or macros whose current signature makes them hard or impossible to extend in the future: backwards compatible extensions would either make the interface intolerably hairy, or are sometimes outright impossible. - __Internal Interfaces__ SBCL has several internal interfaces that were never meant to be used in user code -- or at least never meant to be used in user code unwilling to track changes to SBCL internals. Ideally, we'd like to be free to refactor our own internals as we please, without even going through the hassle of deprecating things. Sometimes, however, it turns out that our internal interfaces have several external users who aren't using them advisedly, but due to misunderstandings regarding their status or stability. Consider a deprecated internal interface a reminder for SBCL maintainers not to delete the thing just yet, even though it is seems unused -- because it has external users. When internal interfaces are deprecated we try our best to provide supported alternatives. - __Aesthetics & Ease of Maintenance__ Sometimes an interface isn't broken or internal but just inconsistent somehow. This mostly happens only with historical interfaces inherited from CMUCL which often haven't been officially supported in SBCL before, or with new extensions to SBCL that haven't been around for very long in the first place. The alternative would be to keep the suboptimal version around forever, possibly alongside an improved version. Sometimes we may do just that, but because every line of code comes with a maintenance cost, sometimes we opt to deprecate the suboptimal version instead: SBCL doesn't have infinite developer resources. We also believe that sometimes cleaning out legacy interfaces helps keep the whole system more comprehensible to users, and makes introspective tools such as APROPOS more useful.") (defsection @the-deprecation-pipeline (:title "The Deprecation Pipeline") "SBCL uses a _deprecation pipeline_ with multiplestages: as time time goes by, deprecated things move from earlier stages of deprecation to later stages before finally being removed. The intention is making users aware of necessary changes early but allowing a migration to new interfaces at a reasonable pace. Deprecation proceeds in three stages, each lasting approximately a year. In some cases it might move slower or faster, but one year per stage is what we aim at in general. During each stage warnings (and errors) of increasing severity are signaled, which note that the interface is deprecated, and point users towards any replacements when applicable. - __Early Deprecation__ During early deprecation the interface is kept in working condition. However, when a thing in this deprecation stage is used, an SB-EXT:EARLY-DEPRECATION-WARNING, which is a STYLE-WARNING, is signaled at compile-time. The internals may change at this stage: typically because the interface is re-implemented on top of its successor. While we try to keep things as backwards-compatible as feasible (taking maintenance costs into account), sometimes semantics change slightly. For example, when the spinlock API was deprecated, spinlock objects ceased to exist, and the whole spinlock API became a synonym for the mutex API -- so code using the spinlock API continued working but silently switched to mutexes instead. However, if someone relied on (typep lock 'spinlock) returning NIL for a mutexes, trouble could ensue. - __Late Deprecation__ During late deprecation the interface remains as it was during early deprecation, but the compile-time warning is upgraded: when a thing in this deprecation stage is used, a SB-EXT:LATE-DEPRECATION-WARNING, which is a full WARNING, is signaled at compile-time. - __Final Deprecation__ During final deprecation the symbols still exist. However, when a thing in this deprecation stage is used, a SB-EXT:FINAL-DEPRECATION-WARNING, which is a full WARNING, is signaled at compile-time and an ERROR is signaled at run-time. - __After Final Deprecation__ The interface is deleted entirely.") (defsection @deprecation-conditions (:title "Deprecation Conditions") "SB-EXT:DEPRECATION-CONDITION is the superclass of all deprecation-related warning and error conditions. All common slots and readers are defined in this condition class." (sb-ext:deprecation-condition condition) (sb-ext:early-deprecation-warning condition) (sb-ext:late-deprecation-warning condition) (sb-ext:final-deprecation-warning condition) (sb-ext:deprecation-error condition)) (defsection @introspecting-deprecation-information (:title "Introspecting Deprecation Information") "The deprecation status of functions and variables can be inspected using the SB-CLTL2:FUNCTION-INFORMATION and SB-CLTL2:VARIABLE-INFORMATION functions provided by the `SB-CLTL2` contributed module.") (defsection @deprecation-declaration (:title "Deprecation Declaration") "The SB-EXT:DEPRECATED declaration can be used to declare objects in various namespaces as deprecated. > _Note_: See the `namespace` CLHS glossary entry in the glossary of > the Common Lisp HyperSpec.)" (sb-ext:deprecated declaration)) (defsection @deprecation-examples (:title "Deprecation Examples") "Marking functions as deprecated: (defun foo ()) (defun bar ()) (declaim (deprecated :early (\"my-system\" \"1.2.3\") (function foo :replacement bar))) ;; Remember: do not define the actual function or variable in case of ;; :final deprecation: (declaim (deprecated :final (\"my-system\" \"1.2.3\") (function fez :replacement whoop))) Attempting to use the deprecated functions: (defun baz () (foo)) | STYLE-WARNING: The function CL-USER::FOO has been deprecated... => BAZ (baz) => NIL ; no error (defun danger () (fez)) | WARNING: The function CL-USER::FEZ has been deprecated... => DANGER (danger) |- ERROR: The function CL-USER::FEZ has been deprecated...") (defsection @deprecated-interfaces-in-sbcl (:title "Deprecated Interfaces in SBCL") "This sections lists legacy interfaces in various stages of deprecation." (@list-of-deprecated-interfaces section) (@historical-interfaces section)) (defsection @list-of-deprecated-interfaces (:title "List of Deprecated Interfaces") (@early-deprecation section) (@late-deprecation section) (@final-deprecation section)) (defsection @early-deprecation (:title "Early Deprecation") "- `SOCKINT::WIN32-*` Deprecated in favor of the corresponding prefix-less functions (e.g. `SOCKINT::BIND` replaces `SOCKINT::WIN32-BIND`) as of 1.2.10 in March 2015. Expected to move into late deprecation in August 2015. - SB-UNIX:UNIX-EXIT Deprecated as of 1.0.56.55 in May 2012. Expected to move into late deprecation in May 2013. When the SBCL process termination was refactored, SB-UNIX:UNIX-EXIT ceased to be used internally. Since `SB-UNIX` is an internal package not intended for user code to use, and since we're slowly in the process of refactoring things to be less Unix-oriented, SB-UNIX:UNIX-EXIT was initially deleted as it was no longer used. Unfortunately it became apparent that it was used by several external users, so it was re-instated in deprecated form. While the cost of keeping SB-UNIX:UNIX-EXIT indefinitely is trivial, the ability to refactor our internals is important, so its deprecation was taken as an opportunity to highlight that `SB-UNIX` is an internal package and `SB-POSIX` should be used by user-programs instead -- or alternatively calling the foreign function directly if the desired interface doesn't for some reason exist in `SB-POSIX`. __Remedy__ For code needing to work with legacy SBCLs, use e.g. `SYSTEM-EXIT`. In modern SBCLs, simply call either SB-POSIX:EXIT or SB-EXT:EXIT with appropriate arguments. - `SB-C::MERGE-TAIL-CALLS` compiler policy Deprecated as of 1.0.53.74 in November 2011. Expected to move into late deprecation in November 2012. This compiler policy was never functional: SBCL has always merged tail calls when it could, regardless of this policy setting. (It was also never officially supported, but several code-bases have historically used it.) __Remedy__ Simply remove the policy declarations. They were never necessary: SBCL always merged tail-calls when possible. To disable tail merging, structure the code to avoid the tail position instead. - The Spinlock API Deprecated as of 1.0.53.11 in August 2011. Expected to move into late deprecation in August 2012. Spinlocks were an internal interface but had a number of external users and were hence deprecated instead of being simply deleted. Affected symbols: SB-THREAD::SPINLOCK, SB-THREAD::MAKE-SPINLOCK, SB-THREAD::WITH-SPINLOCK, SB-THREAD::WITH-RECURSIVE-SPINLOCK, SB-THREAD::GET-SPINLOCK, SB-THREAD::RELEASE-SPINLOCK, SB-THREAD::SPINLOCK-VALUE, and SB-THREAD::SPINLOCK-NAME. __Remedy__ Use the mutex API instead, or implement spinlocks suiting your needs on top of SB-EXT:COMPARE-AND-SWAP, SB-EXT:SPIN-LOOP-HINT, etc. - `SOCKINT::HANDLE->FD`, `SOCKINT::FD->HANDLE` Internally deprecated in 2012. Declared deprecated as of 1.2.10 in March 2015. Expected to move into final deprecation in August 2015.") (defsection @late-deprecation (:title "Late Deprecation") "- SB-THREAD:JOIN-THREAD-ERROR-THREAD and SB-THREAD:INTERRUPT-THREAD-ERROR-THREAD Deprecated in favor of SB-THREAD:THREAD-ERROR-THREAD as of 1.0.29.17 in June 2009. Expected to move into final deprecation in June 2012. __Remedy__ For code that needs to support legacy SBCLs, use e.g.: (defun get-thread-error-thread (condition) #+#.(cl:if (cl:find-symbol \"THREAD-ERROR-THREAD\" :sb-thread) '(and) '(or)) (sb-thread:thread-error-thread condition) #-#.(cl:if (cl:find-symbol \"THREAD-ERROR-THREAD\" :sb-thread) '(and) '(or)) (etypecase condition (sb-thread:join-thread-error (sb-thread:join-thread-error-thread condition)) (sb-thread:interrupt-thread-error (sb-thread:interrupt-thread-error-thread condition)))) - SB-INTROSPECT:FUNCTION-ARGLIST Deprecated in favor of SB-INTROSPECT:FUNCTION-LAMBDA-LIST as of 1.0.24.5 in January 2009. Expected to move into final deprecation in January 2012. Renamed for consistency and aesthetics. Functions have lambda-lists, not arglists. __Remedy__ For code that needs to support legacy SBCLs, use e.g.: (defun get-function-lambda-list (function) #+#.(cl:if (cl:find-symbol \"FUNCTION-LAMBDA-LIST\" :sb-introspect) '(and) '(or)) (sb-introspect:function-lambda-list function) #-#.(cl:if (cl:find-symbol \"FUNCTION-LAMBDA-LIST\" :sb-introspect) '(and) '(or)) (sb-introspect:function-arglist function)) - Stack Allocation Policies Deprecated in favor of SB-EXT:*STACK-ALLOCATE-DYNAMIC-EXTENT* as of 1.0.19.7 in August 2008, and are expected to be removed in August 2012. Affected symbols: `SB-C::STACK-ALLOCATE-DYNAMIC-EXTENT`, `SB-C::STACK-ALLOCATE-VECTOR`, and `SB-C::STACK-ALLOCATE-VALUE-CELLS`. These compiler policies were never officially supported, and turned out the be a flawed design. __Remedy__ For code that needs stack-allocation in legacy SBCLs, conditionalize using: #-#.(cl:if (cl:find-symbol \"*STACK-ALLOCATE-DYNAMIC-EXTENT*\" :sb-ext) '(and) '(or)) (declare (optimize sb-c::stack-allocate-dynamic-extent)) However, unless stack allocation is essential, we recommend simply removing these declarations. Refer to documentation on `SB-EXT:*STACK-ALLOCATE-DYNAMIC*` for details on stack allocation control in modern SBCLs. - `SB-SYS:OUTPUT-RAW-BYTES` Deprecated as of 1.0.8.16 in June 2007. Expected to move into final deprecation in June 2012. Internal interface with some external users. Never officially supported, deemed unnecessary in presence of WRITE-SEQUENCE and bivalent streams. __Remedy__ Use streams with element-type (UNSIGNED-BYTE 8) or :DEFAULT -- the latter allowing both binary and character IO -- in conjunction with WRITE-SEQUENCE.") (defsection @final-deprecation (:title "Final Deprecation") "No interfaces are currently in final deprecation.") (defsection @historical-interfaces (:title "Historical Interfaces") "The following is a partial list of interfaces present in historical versions of SBCL, which have since then been deleted. - `SB-KERNEL:INSTANCE-LAMBDA` Historically needed for CLOS code. Deprecated as of 0.9.3.32 in August 2005. Deleted as of 1.0.47.8 in April 2011. Plain LAMBDA can be used where `SB-KERNEL:INSTANCE-LAMBDA` used to be needed. - `SB-ALIEN:DEF-ALIEN-ROUTINE`, `SB-ALIEN:DEF-ALIEN-VARIABLE`, `SB-ALIEN:DEF-ALIEN-TYPE` Inherited from CMUCL, naming convention not consistent with preferred SBCL style. Deprecated as of 0.pre7.90 in December 2001. Deleted as of 1.0.9.17 in September 2007. Replaced by SB-ALIEN:DEFINE-ALIEN-ROUTINE, SB-ALIEN:DEFINE-ALIEN-VARIABLE, and SB-ALIEN:DEFINE-ALIEN-TYPE.")