Erlang Language Bit Syntax: Defaults Rewrite of the docs.
Example
4.4 Defaults
[Beginning omitted: <<3.14>> isn't even legal syntax.]
The default Size depends on the type. For integer it is 8. For float it is 64. For binary it is the actual size of the specified binary:
1> Bin = << 17/integer, 3.2/float, <<97, 98, 99>>/binary >>. <<17,64,9,153,153,153,153,153,154,97,98,99>> ^ |<-------------------------->|<------>|
| float=64 binary=24
integer=8
2> size(Bin). % Returns the number of bytes: 12 % 8 bits + 64 bits + 3*8 bits = 96 bits => 96/8 = 12 bytesIn matching, a binary segment without a Size is only allowed at the end of the pattern, and the default Size is the rest of the binary on the right hand side of the match:
25> Bin = <<97, 98, 99>>. <<"abc">> 26> << X/integer, Rest/binary >> = Bin. <<"abc">> 27> X. 97 28> Rest. <<"bc">>All other segments with type binary in a pattern must specify a Size:
12> Bin = <<97, 98, 99, 100>>. <<"abcd">> 13> << B:1/binary, X/integer, Rest/binary >> = Bin. %'unit' defaults to 8 for <<"abcd">> %binary type, total segment size is Size * unit 14> B. <<"a">> 15> X. 98 16> Rest. <<"cd">> 17> << B2/binary, X2/integer, Rest2/binary >> = Bin. * 1: a binary field without size is only allowed at the end of a binary pattern
