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Re: Automatic null checks

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supercat@casperkitty.com writes:

> On Sunday, January 1, 2017 at 11:53:30 AM UTC-6, Thiago Adams wrote:
>> I am implementing the concept of null checking in 
>> my static analyser.
>
> A fundamental difficulty with non-nullable pointer/reference types, which
> renders absurd the notion that null pointers were a "billion-dollar mistake",
> is that it will often be necessary to read some items out of an array of
> pointers before all members of the array have been written, and *something*
> has to happen if code attempts to read from an array element which has not
> been written.

But something can (and should) always be written.  Other languages deal
with this using a discriminated union or "maybe" type of some sort and
the array is always initially filled with values of the "nothing" type.
The only way to access an element is with a type-checked case statement
(or expression) of some form:

  for (int i = 0; i < A.len; i++)
    case A[i] of
      type nothing: skip;
      type some p: process_pointer(p);

Apologies if this syntax is not clear, I just make it up.

The key difference is that the compiler can check that a NULL pointer is
never used.

<skip>
-- 
Ben.

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Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-01 09:53 -0800
  Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-01 10:16 -0800
    Re: Automatic null checks Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-01 19:26 +0000
      Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-02 05:56 -0800
        Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-02 08:26 -0800
    Re: Automatic null checks jacobnavia <jacob@jacob.remcomp.fr> - 2017-01-01 22:39 +0100
  Re: Automatic null checks supercat@casperkitty.com - 2017-01-01 14:24 -0800
    Re: Automatic null checks Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-01 23:00 +0000
      Re: Automatic null checks supercat@casperkitty.com - 2017-01-01 16:42 -0800
        Re: Automatic null checks Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-02 02:08 +0000
          Re: Automatic null checks supercat@casperkitty.com - 2017-01-02 09:38 -0800
            Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-02 10:25 -0800
            Re: Automatic null checks Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-02 18:48 +0000
    Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-02 07:45 -0800
  Re: Automatic null checks Les Cargill <lcargill99@comcast.com> - 2017-01-03 07:11 -0600
    Re: Automatic null checks Thiago Adams <thiago.adams@gmail.com> - 2017-01-03 17:43 -0800

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