Hi,
This is probably a silly question, but while performing a match on bitstring, I got bit (yes!) by a mistake that seems to me easy to do; I found the hard way that the following pattern was not matching as expected: <<FullData:FullLen/binary, _NextChunk>> -> [...], whereas <<FullData:FullLen/binary, _NextChunk/binary>> did.
My question: what would be the meaning of the first form? If no sensible one existed, could it be rejected by the compiler, or at least could a warning be issued?
Thanks in advance for any hint,
Best regards,
Olivier.
The default size is a unsigned byte. If you write this:
<<A,B,C>> = <<1,2,3>>
It makes more sense as the syntax of the left side then reflects the right side.
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Thanks Lukas for your answer! When reading Expressions — Erlang System Documentation v27.2.2 I could see that, in the first form, _NextChunk was falling in the case described as When used in a bit string matching, Value must be a variable, or an integer, float, or string. where it was here an (unbound) variable with no Size or TypeSpecifier. I understand that making it correspond to an integer / unsigned byte is indeed the most logical candidate, but I could not confirm conclusively it by reading this Bit Syntax Expressions section. Maybe I misread it, or it is not so clearly stated there. The point that is a bit less intuitive in that case is that often specifying a mute variable is interpreted as a request to “match anything”.
Thanks again!
Olivier.
I too cannot find any place where the default type is described, only what the deafult sizes are for the different types. A PR adding that information would be most welcome.