class Prism::CodeUnitsCache
A cache that can be used to quickly compute code unit offsets from byte offsets. It purposefully provides only a single []
method to access the cache in order to minimize surface area.
Note that there are some known issues here that may or may not be addressed in the future:
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The first is that there are issues when the cache computes values that are not on character boundaries. This can result in subsequent computations being off by one or more code units.
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The second is that this cache is currently unbounded. In theory we could introduce some kind of LRU cache to limit the number of entries, but this has not yet been implemented.
Public Class Methods
Source
# File lib/prism/parse_result.rb, line 198 def initialize(source, encoding) @source = source @counter = if encoding == Encoding::UTF_16LE || encoding == Encoding::UTF_16BE UTF16Counter.new(source, encoding) else LengthCounter.new(source, encoding) end @cache = {} @offsets = [] end
Initialize a new cache with the given source and encoding.
Public Instance Methods
Source
# File lib/prism/parse_result.rb, line 212 def [](byte_offset) @cache[byte_offset] ||= if (index = @offsets.bsearch_index { |offset| offset > byte_offset }).nil? @offsets << byte_offset @counter.count(0, byte_offset) elsif index == 0 @offsets.unshift(byte_offset) @counter.count(0, byte_offset) else @offsets.insert(index, byte_offset) offset = @offsets[index - 1] @cache[offset] + @counter.count(offset, byte_offset - offset) end end
Retrieve the code units offset from the given byte offset.