Clojure

transient blows up when passed a vector created by subvec

Details

  • Type: Defect Defect
  • Status: Open Open
  • Priority: Minor Minor
  • Resolution: Unresolved
  • Affects Version/s: Backlog
  • Fix Version/s: Release 1.6
  • Component/s: None
  • Labels:
    None
  • Patch:
    Code and Test
  • Approval:
    Vetted

Description

Subvectors created with subvec from a PersistentVector cannot be made transient:

user=> (transient (subvec [1 2 3 4] 2))
ClassCastException clojure.lang.APersistentVector$SubVector cannot be cast to clojure.lang.IEditableCollection  clojure.core/transient (core.clj:2864)

Activity

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Stuart Sierra added a comment -

Confirmed. APersistentVector$SubVector does not implement IEditableCollection.

The current implementation of TransientVector depends on implementation details of PersistentVector, so it is not a trivial fix. The simplest fix might be to implement IEditableCollection.asTransient in SubVector by creating a new PersistentVector, but I do not know the performance implications.

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Stuart Sierra added a comment - Confirmed. APersistentVector$SubVector does not implement IEditableCollection. The current implementation of TransientVector depends on implementation details of PersistentVector, so it is not a trivial fix. The simplest fix might be to implement IEditableCollection.asTransient in SubVector by creating a new PersistentVector, but I do not know the performance implications.
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Gary Fredericks added a comment -

We could get the same performance characteristics as SubVector by creating a TransientSubVector based on an underlying TransientVector, right?

Preparing a patch to that effect.

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Gary Fredericks added a comment - We could get the same performance characteristics as SubVector by creating a TransientSubVector based on an underlying TransientVector, right? Preparing a patch to that effect.
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Gary Fredericks added a comment -

Text from the commit msg:

Made two assumptions:

  • It's okay for TransientSubVector to delegate the ensureEditable
    functionality to the underlying TransientVector (sometimes
    explicitely, sometimes implicitely) – calling ensureEditable
    explicitely also requires that the field for the underlying vector
    be the concrete TransientVector type rather than the
    ITransientVector interface.
  • When an operation that would throw an exception on a
    PersistentVector happens from the wrong thread (or after
    persistent!), we throw that exception rather than the
    IllegalAccessError that transients throw when accessed
    inappropriately.
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Gary Fredericks added a comment - Text from the commit msg: Made two assumptions:
  • It's okay for TransientSubVector to delegate the ensureEditable functionality to the underlying TransientVector (sometimes explicitely, sometimes implicitely) – calling ensureEditable explicitely also requires that the field for the underlying vector be the concrete TransientVector type rather than the ITransientVector interface.
  • When an operation that would throw an exception on a PersistentVector happens from the wrong thread (or after persistent!), we throw that exception rather than the IllegalAccessError that transients throw when accessed inappropriately.

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Dates

  • Created:
    Updated:
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