Enum forest_filecoin::ipld::selector::Selector
source · pub enum Selector {
Matcher,
ExploreAll {
next: Box<Selector>,
},
ExploreFields {
fields: IndexMap<String, Selector>,
},
ExploreIndex {
index: usize,
next: Box<Selector>,
},
ExploreRange {
start: usize,
end: usize,
next: Box<Selector>,
},
ExploreRecursive {
sequence: Box<Selector>,
limit: RecursionLimit,
stop_at: Option<Condition>,
current: Option<Box<Selector>>,
},
ExploreUnion(Vec<Selector>),
ExploreRecursiveEdge,
}
Expand description
Selectors are expressions that identify and select a subset of data from an IPLD DAG. Selectors are themselves IPLD and can be serialized and de-serialized as such.
Variants§
Matcher
Matcher
marks a node to be included in the “result” set.
(All nodes traversed by a selector are in the “covered” set (which is
a.k.a. “the Merkle proof”); the “result” set is a subset of the
“covered” set.)
In libraries using selectors, the “result” set is typically provided to some user-specified callback.
A selector tree with only “explore*”-type selectors and no Matcher
selectors is valid; it will just generate a “covered” set of nodes
and no “result” set.
ExploreAll
ExploreAll
is similar to a *
– it traverses all elements of an
array, or all entries in a map, and applies a next selector to the
reached nodes.
ExploreFields
ExploreFields
traverses named fields in a map (or equivalently,
structure, if traversing on typed/schema nodes) and applies a next
selector to the reached nodes.
Note that a concept of exploring a whole path (e.g. “path/to/file”) can
be represented as a set of three nested ExploreFields
selectors,
each specifying one field.
Fields insertion order is maintained and traversed using that order.
ExploreIndex
ExploreIndex
traverses a specific index in a list, and applies a next
selector to the reached node.
ExploreRange
ExploreRange
traverses a list, and for each element in the range
specified, will apply a next selector to those reached nodes.
ExploreRecursive
ExploreRecursive
traverses some structure recursively.
To guide this exploration, it uses a “sequence”, which is another
Selector tree; some leaf node in this sequence should contain an
ExploreRecursiveEdge
selector, which denotes the place recursion
should occur.
In implementation, whenever evaluation reaches an ExploreRecursiveEdge
marker in the recursion sequence’s Selector tree, the implementation
logically produces another new Selector which is a copy of the
original ExploreRecursive
selector, but with a decremented depth
parameter for limit (if limit is of type depth), and continues
evaluation.
It is not valid for an ExploreRecursive
selector’s sequence to contain
no instances of ExploreRecursiveEdge
; it is valid for it to contain
more than one ExploreRecursiveEdge
.
ExploreRecursive
can contain a nested ExploreRecursive
!
This is comparable to a nested for-loop.
In these cases, any ExploreRecursiveEdge
instance always refers to the
nearest parent ExploreRecursive
(in other words,
ExploreRecursiveEdge
can be thought of like the ‘continue’
statement, or end of a for-loop body; it is not a goto
statement).
Be careful when using ExploreRecursive
with a large depth limit
parameter; it can easily cause very large traversals (especially if
used in combination with selectors like ExploreAll
inside the
sequence).
limit is a union type – it can have an integer depth value (key “depth”) or no value (key “none”). If limit has no value it is up to the implementation library using selectors to identify an appropriate max depth as necessary so that recursion is not infinite
Fields
limit: RecursionLimit
ExploreUnion(Vec<Selector>)
ExploreUnion
allows selection to continue with two or more distinct
selectors while exploring the same tree of data.
ExploreUnion
can be used to apply a Matcher
on one node (causing it
to be considered part of a (possibly labeled) result set), while
simultaneously continuing to explore deeper parts of the tree with
another selector, for example.
ExploreRecursiveEdge
ExploreRecursiveEdge
is a special sentinel value which is used to mark
the end of a sequence started by an ExploreRecursive
selector: the
recursion goes back to the initial state of the earlier
ExploreRecursive
selector, and proceeds again (with a decremented
maxDepth
value).
An ExploreRecursive
selector that doesn’t contain an
ExploreRecursiveEdge
is nonsensical. Containing more than one
ExploreRecursiveEdge
is valid. An ExploreRecursiveEdge
without
an enclosing ExploreRecursive
is an error.
Trait Implementations§
source§impl<'de> Deserialize<'de> for Selector
impl<'de> Deserialize<'de> for Selector
source§fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>where
__D: Deserializer<'de>,
fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>where
__D: Deserializer<'de>,
source§impl PartialEq for Selector
impl PartialEq for Selector
impl StructuralPartialEq for Selector
Auto Trait Implementations§
impl Freeze for Selector
impl RefUnwindSafe for Selector
impl Send for Selector
impl Sync for Selector
impl Unpin for Selector
impl UnwindSafe for Selector
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