Trait spacetimedb_table::var_len::VarLenMembers
source · pub unsafe trait VarLenMembers {
type Iter<'this, 'row>: Iterator<Item = &'row MaybeUninit<VarLenRef>>
where Self: 'this;
type IterMut<'this, 'row>: Iterator<Item = &'row mut MaybeUninit<VarLenRef>>
where Self: 'this;
// Required methods
unsafe fn visit_var_len_mut<'this, 'row>(
&'this self,
row: &'row mut Bytes
) -> Self::IterMut<'this, 'row>;
unsafe fn visit_var_len<'this, 'row>(
&'this self,
row: &'row Bytes
) -> Self::Iter<'this, 'row>;
}Expand description
A visitor object which can iterate over the var-len slots in a row.
Each var-len visitor is specialized to a particular row type,
though implementors of VarLenMembers decide whether this specialization
is per instance or per type.
The trivial implementor of VarLenMembers is AlignedVarLenOffsets,
which stores the offsets of var-len members in a particular row type in a slice,
and uses pointer arithmetic to return references to them.
§Safety
Self::visit_var_lenandSelf::visit_var_len_mutmust visit the same set ofVarLenRefs in the same order. Various consumers inPageand friends depend on this and the previous requirement.
Required Associated Types§
sourcetype Iter<'this, 'row>: Iterator<Item = &'row MaybeUninit<VarLenRef>>
where
Self: 'this
type Iter<'this, 'row>: Iterator<Item = &'row MaybeUninit<VarLenRef>> where Self: 'this
The iterator type returned by VarLenMembers::visit_var_len.
sourcetype IterMut<'this, 'row>: Iterator<Item = &'row mut MaybeUninit<VarLenRef>>
where
Self: 'this
type IterMut<'this, 'row>: Iterator<Item = &'row mut MaybeUninit<VarLenRef>> where Self: 'this
The iterator type returned by VarLenMembers::visit_var_len_mut.
Required Methods§
sourceunsafe fn visit_var_len_mut<'this, 'row>(
&'this self,
row: &'row mut Bytes
) -> Self::IterMut<'this, 'row>
unsafe fn visit_var_len_mut<'this, 'row>( &'this self, row: &'row mut Bytes ) -> Self::IterMut<'this, 'row>
Treats row as storage for a row of the particular type handled by self,
and iterates over the (possibly uninitialized) VarLenRefs within it.
Callers are responsible for maintaining whether var-len members have been initialized.
§Safety
-
rowmust be properly aligned for the row type. This alignment constraint should be defined (and documented!) by the implementor ofVarLenMembers. -
rowmust further be a slice of exactly the number of bytes of the row type. Implementors may or may not check this property viadebug_assert!, but callers must always ensure it for safety. These invariants allow us to construct references toVarLenRefs inside the slice.Note that
Iterator::nextis a safe function, so it must always be valid to advance an iterator to its end. -
All callers of
visit_var_lenon a particularrowmust visit the same set ofVarLenRefs in the same order, though they may do so through different implementors ofVarLenMembers. E.g. it would be valid to use anAlignedVarLenOffsetsto initialize a row, then later read from it using a hypothetical optimized JITted visitor, provided the JITted visitor visited the same set of offsets.
sourceunsafe fn visit_var_len<'this, 'row>(
&'this self,
row: &'row Bytes
) -> Self::Iter<'this, 'row>
unsafe fn visit_var_len<'this, 'row>( &'this self, row: &'row Bytes ) -> Self::Iter<'this, 'row>
Treats row as storage for a row of the particular type handled by self,
and iterates over the (possibly uninitialized) VarLenRefs within it.
Callers are responsible for maintaining whether var-len members have been initialized.
§Safety
-
rowmust be properly aligned for the row type. This alignment constraint should be defined (and documented!) by the implementor ofVarLenMembers. -
rowmust further be a slice of exactly the number of bytes of the row type. Implementors may or may not check this property viadebug_assert!, but callers must always ensure it for safety. These invariants allow us to construct references toVarLenRefs inside the slice.Note that
Iterator::nextis a safe function, so it must always be valid to advance an iterator to it end. -
All callers of
visit_var_lenon a particularrowmust visit the same set ofVarLenRefs in the same order, though they may do so through different implementors ofVarLenMembers. E.g. it would be valid to use anAlignedVarLenOffsetsto initialize a row, then later read from it using a hypothetical optimized JITted visitor, provided the JITted visitor visited the same set of offsets.