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\chapter{Old-Style Virtual Packages}
\label{sec:old-virtuals}
Old-style virtuals are pseudo-packages---they can be depended upon or
installed, but do not exist in the ebuild repository. An old-style
virtual requires several things in the repository: at least one ebuild
must list the virtual in its \t{PROVIDE} variable, and there must be
at least one entry in a profiles \t{virtuals} file listing the default
provider for each profile---see sections~\ref{ebuild-var-provide} and
\ref{sec:profiles-virtuals} for specifics on these two. Old-style virtuals
require special handling as regards dependencies; this is described
below.
All old-style virtuals must use the category \t{virtual}. Not all packages using the \t{virtual}
category may be assumed to be old style virtuals.
\note A \i{new-style} virtual is simply an ebuild which install no files and use its dependency
strings to select providers. By convention, and to ease migration, these are also placed in the
\t{virtual} category.
\section{Dependencies on virtual packages}
When a dependency on a virtual package is encountered, it must be
resolved into a real package before it can be satisfied. There are two
factors that affect this process: whether a package providing the
virtual is installed, and the \t{virtuals} file in the active profile
(section~\ref{sec:profiles-virtuals}). If a package is already installed
which satisfies the virtual requirement (via \t{PROVIDE}), then it
should be used to satisfy the dependency. Otherwise, the profiles
\t{virtuals} file (section~\ref{sec:profiles-virtuals}) should be
consulted to choose an appropriate provider.
Dependencies on old style virtuals must not use any kind of version restriction.
Blocks on provided virtuals have special behaviour documented in section~\ref{provided-blocks}.
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