[erlang-questions] Binary pattern matching inconsistencies with R12B
Fri Feb 29 23:04:31 CET 2008
On Fri, Feb 29, 2008 at 01:00:29PM -0500, Rusty Klophaus wrote:
> You may want to try specifying a size for the variables D, N, and C.
> For example: scan(<<C:8/integer, Rest/binary>>, TokAcc)
> According to the manual: "In matching, this default value is only valid
> for the very last element. All other bit string or binary elements in the
> matching must have a size specification."
> It's possible that the lack of a size is confusing things.
> Hope that helps,
Cheers Rusty, I took a shot at that, but no dice I'm afraid.
Actually, I ran into a problem on another project that led me to
this passage last week. I was trying to write something like
<<Data/binary, Pad:8>> = Payload.
but the compiler was complaing (as compilers do). What it was
trying to tell me was that a binary type must have a length
field unless it appears at the end of a <<binary>> pattern.
Sorry, when speaking about this stuff the term binary inevitably
gets overloaded. In essence, it was telling me I had to
do something like:
Length = size(Payload) - 1,
<<Data:(Length)/binary, Pad:8>> = Payload.
Something like that anyway. That's what the passage you quoted is
about - it's talking about using the binary type within a pattern.
You must specify a length with it unless it's at the end of the
Also, the defaults for items in a pattern are size 8 and type
integer - so I think my code is safe. Truth be told, if I
had to write that stuff for each term I'd probably just convert
the thing to a list and do matching that way. Yeah, I'm that
Thanks again Rusty,
More information about the erlang-questions