Nix/src/libstore/derived-path-map.hh
John Ericson ac89bb064a Split up util.{hh,cc}
All OS and IO operations should be moved out, leaving only some misc
portable pure functions.

This is useful to avoid copious CPP when doing things like Windows and
Emscripten ports.

Newly exposed functions to break cycles:

 - `restoreSignals`
 - `updateWindowSize`
2023-11-05 12:20:02 -05:00

97 lines
2.6 KiB
C++

#pragma once
///@file
#include "types.hh"
#include "derived-path.hh"
namespace nix {
/**
* A simple Trie, of sorts. Conceptually a map of `SingleDerivedPath` to
* values.
*
* Concretely, an n-ary tree, as described below. A
* `SingleDerivedPath::Opaque` maps to the value of an immediate child
* of the root node. A `SingleDerivedPath::Built` maps to a deeper child
* node: the `SingleDerivedPath::Built::drvPath` is first mapped to a a
* child node (inductively), and then the
* `SingleDerivedPath::Built::output` is used to look up that child's
* child via its map. In this manner, every `SingleDerivedPath` is
* mapped to a child node.
*
* @param V A type to instantiate for each output. It should probably
* should be an "optional" type so not every interior node has to have a
* value. `* const Something` or `std::optional<Something>` would be
* good choices for "optional" types.
*/
template<typename V>
struct DerivedPathMap {
/**
* A child node (non-root node).
*/
struct ChildNode {
/**
* Value of this child node.
*
* @see DerivedPathMap for what `V` should be.
*/
V value;
/**
* The map type for the root node.
*/
using Map = std::map<OutputName, ChildNode>;
/**
* The map of the root node.
*/
Map childMap;
DECLARE_CMP(ChildNode);
};
/**
* The map type for the root node.
*/
using Map = std::map<StorePath, ChildNode>;
/**
* The map of root node.
*/
Map map;
DECLARE_CMP(DerivedPathMap);
/**
* Find the node for `k`, creating it if needed.
*
* The node is referred to as a "slot" on the assumption that `V` is
* some sort of optional type, so the given key can be set or unset
* by changing this node.
*/
ChildNode & ensureSlot(const SingleDerivedPath & k);
/**
* Like `ensureSlot` but does not create the slot if it doesn't exist.
*
* Read the entire description of `ensureSlot` to understand an
* important caveat here that "have slot" does *not* imply "key is
* set in map". To ensure a key is set one would need to get the
* child node (with `findSlot` or `ensureSlot`) *and* check the
* `ChildNode::value`.
*/
ChildNode * findSlot(const SingleDerivedPath & k);
};
DECLARE_CMP_EXT(
template<>,
DerivedPathMap<std::set<std::string>>::,
DerivedPathMap<std::set<std::string>>);
DECLARE_CMP_EXT(
template<>,
DerivedPathMap<std::set<std::string>>::ChildNode::,
DerivedPathMap<std::set<std::string>>::ChildNode);
}