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Diffstat (limited to 'doc/lispref/functions.texi')
| -rw-r--r-- | doc/lispref/functions.texi | 31 |
1 files changed, 18 insertions, 13 deletions
diff --git a/doc/lispref/functions.texi b/doc/lispref/functions.texi index c6188ce466d..c3e5dc0eb5b 100644 --- a/doc/lispref/functions.texi +++ b/doc/lispref/functions.texi @@ -1225,7 +1225,7 @@ This form defines a method like @code{cl-defmethod} does. @end table @end defmac -@defmac cl-defmethod name [qualifier] arguments &rest [docstring] body +@defmac cl-defmethod name [qualifier] arguments [&context (expr spec)@dots{}] &rest [docstring] body This macro defines a particular implementation for the generic function called @var{name}. The implementation code is given by @var{body}. If present, @var{docstring} is the documentation string @@ -1246,21 +1246,26 @@ This specializer requires the argument be @code{eql} to the given @item (head @var{object}) The argument must be a cons cell whose @code{car} is @code{eql} to @var{object}. -@item @var{struct-tag} -The argument must be an instance of a class named @var{struct-tag} +@item @var{struct-type} +The argument must be an instance of a class named @var{struct-type} defined with @code{cl-defstruct} (@pxref{Structures,,, cl, Common Lisp -Extensions for GNU Emacs Lisp}), or of one of its parent classes. +Extensions for GNU Emacs Lisp}), or of one of its child classes. @end table -Alternatively, the argument specializer can be of the form -@code{&context (@var{expr} @var{spec})}, in which case the value of -@var{expr} must be compatible with the specializer provided by -@var{spec}; @var{spec} can be any of the forms described above. In -other words, this form of specializer uses the value of @var{expr} -instead of arguments for the decision whether the method is -applicable. For example, @code{&context (overwrite-mode (eql t))} -will make the method compatible only when @code{overwrite-mode} is -turned on. +Method definitions can make use of a new argument-list keyword, +@code{&context}, which introduces extra specializers that test the +environment at the time the method is run. This keyword should appear +after the list of required arguments, but before any @code{&rest} or +@code{&optional} keywords. The @code{&context} specializers look much +like regular argument specializers---(@var{expr} @var{spec})---except +that @var{expr} is an expression to be evaluated in the current +context, and the @var{spec} is a value to compare against. For +example, @code{&context (overwrite-mode (eql t))} will make the method +applicable only when @code{overwrite-mode} is turned on. The +@code{&context} keyword can be followed by any number of context +specializers. Because the context specializers are not part of the +generic function's argument signature, they may be omitted in methods +that don't require them. The type specializer, @code{(@var{arg} @var{type})}, can specify one of the @dfn{system types} in the following list. When a parent type |