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Support creating and matching bitstrings that are in fact binaries (size divisible by 8) #1978

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Support creating and matching bitstrings that are in fact binaries (size divisible by 8) #1978

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@mat-hek mat-hek commented Nov 13, 2025 •
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In some cases, there's generic code that uses the bitstring modifier because it needs to work for both bitstrings and binaries, for example in erl_eval. Currently such code doesn't work even if no actual bitstrings are involved, and this PR attempts to fix it. In other words, this now works:

defmodule Foo do
  def pattern_match(x, s) do
    case x do
      <<a::bitstring-size(s), b::bitstring>> ->
        {a, b}

      _ ->
        :no_match
    end
  end

  def create(y, s) do
    <<y::bitstring-size(s), 123>>
  end
end

Foo.pattern_match(<<234, 123, 2>>, 16)
# => {<<234, 123>>, <<2>>}
Foo.create(<<234, 123, 2>>, 16)
# => <<234, 123, 123>>

TODO:

  • add tests
  • adjust jit.erl

@mat-hek mat-hek force-pushed the mf/upstream-support-aligned-bitstrings branch from d622626 to bb34fe8 Compare November 13, 2025 14:35
@mat-hek mat-hek force-pushed the mf/upstream-support-aligned-bitstrings branch from bb34fe8 to 7bb58f2 Compare November 13, 2025 14:37
@mat-hek mat-hek mentioned this pull request Nov 14, 2025
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@mat-hek