11 Packages 11.1 Package Concepts 11.1.1 Introduction to Packages 220.127.116.11 Symbols in a Package
18.104.22.168.5 Prevention of Name Conflicts in Packages
Within one package, any particular name can refer to at most one
symbol. A name conflict is said to occur when there would be more than
one candidate symbol. Any time a name conflict is about to occur,
a correctable error is signaled.
The following rules apply to name conflicts:
Name conflicts are detected when they become possible, that is, when the
package structure is altered. Name
conflicts are not checked during every name lookup.
If the same symbol is accessible to a package
through more than one path, there is no name conflict.
A symbol cannot conflict with itself.
Name conflicts occur only between distinct symbols with
the same name (under string=).
- -- Every package has a list of shadowing symbols.
A shadowing symbol takes precedence over any other symbol of
the same name that would otherwise be accessible in the package.
A name conflict involving a shadowing symbol is always resolved in favor of
the shadowing symbol, without signaling an error (except for one
exception involving import).
See shadow and shadowing-import.
The functions use-package, import, and
export check for name conflicts.
shadow and shadowing-import
never signal a name-conflict error.
unuse-package and unexport
do not need to do any name-conflict checking.
unintern does name-conflict checking only when a symbol
being uninterned is a shadowing symbol.
Giving a shadowing symbol to unintern
can uncover a name conflict that had
previously been resolved by the shadowing.
Package functions signal name-conflict errors of type package-error before making any
change to the package structure. When multiple changes are to be made,
permissible for the implementation to process each change separately.
For example, when export is given a
aborting from a name
conflict caused by the second symbol
in the list might still export the
first symbol in the list.
However, a name-conflict error caused by export
of a single symbol will be signaled before
that symbol's accessibility in any package is changed.
Continuing from a name-conflict error must offer the user a chance to
resolve the name conflict in favor of either of the candidates. The
structure should be altered to reflect the resolution of the
name conflict, via shadowing-import,
A name conflict in use-package between a symbol
present in the using package and an external symbol of the used
package is resolved in favor of the first symbol by making it a
shadowing symbol, or in favor of the second symbol by uninterning
the first symbol from the using package.
A name conflict in export or unintern
due to a package's inheriting two distinct symbols
with the same name (under string=)
from two other packages can be resolved in
favor of either symbol by importing it into the using
package and making it a shadowing symbol,
just as with use-package.