[erlang-questions] Dialyzer and numeric range values

zxq9 <>
Wed Nov 1 11:47:32 CET 2017


If I give a typespec

-type foo() :: 10..14.

Dialyzer will show me

10 | 11 | 12 | 13 | 14

I can see this is inclusive.

If I give a typespec like

4..65

Dialyzer will show me

1..255

If I give a typespec

3..500

Dialyzer will show me

1..1114111

Which is hugely different than what I want.

Which also winds up meaning that 0..16#ffff, which should be the legal range for ports, winds up being interpreted as type char(), which happens to be 0..16#10ffff which is totally bizarre.

In fact, the docs for inet show me this definition:

ip6_address() =
    {0..65535,
     0..65535,
     0..65535,
     0..65535,
     0..65535,
     0..65535,
     0..65535,
     0..65535}

( http://erlang.org/doc/man/inet.html )

which I am shown Dialyzer interpreting as

{char(), char(), char(), char(), char(), char(), char(), char()}

and I can see the actual definition of char in the docs is indeed

-type char() :: 0..16#10ffff.

( erlang.org/documentation/doc-5.8/doc/reference_manual/typespec.html )

What is going on here? Is this a new thing with R20's Dialyzer, or have I just never noticed these multi-byte leaps in value range resolution?

-Craig


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