dip1000 rule 5

[sclytrack]

On Monday, 26 November 2018 at 09:10:23 UTC, sclytrack wrote:
> On Sunday, 25 November 2018 at 19:22:36 UTC, sclytrack wrote:
>> There are 4 rules listed.
>>
>> https://github.com/dlang/DIPs/blob/master/DIPs/DIP1000.md
>>
>>
>>
>>
>> What is rule 5?
>>
>>
>> int* global_ptr;
>>
>> void abc() {
>>     scope int* a;
>>     int* b;
>>     scope int* c = a;      // Error, rule 5
>>     scope int* d = b;      // Ok
>>     int* i = a;            // Ok, scope is inferred for i
>>     global_ptr = d;        // Error, lifetime(d) < 
>> lifetime(global_ptr)
>>     global_ptr = i;        // Error, lifetime(i) < 
>> lifetime(global_ptr)
>>     int* j;
>>     global_ptr = j;        // Ok, j is not scope
>> }
>>
>
> ---
>
> Are the following assumptions correct?
>
>
> lifetime(a) < lifetime(b)
> Means that b is older and lives longer than a. Or better, the 
> data that b is pointing
> to is older and lives longer than the one that a is pointing 
> too. With the exception
> of the null pointer which gets unlimited lifetime because it 
> does not corrupt memory.
>
> ---
>
> scope int * a;
>
> The variable gets unlimited lifetime because the value it is 
> pointing is assigned
> null. And that throws exception when trying to access the 
> memory and because
> it does not corrupt memory it is assigned unlimited lifetime. 
> Also once a variable
> is assigned unlimited lifetime, then it retains that unlimited 
> lifetime during
> the entire reachability of the variable.
>
> scope int * c = a;

works

>
> The above is allowed. You are assigning a variable that 
> according to the compiler
> has unlimited lifetime. Therefore the variable c will be 
> handled like it has
> unlimited lifetime by the compiler.
> lifetime(c) <= lifetime(a)
> The dip talks about longer and shorter, but is equal okay too?
>
> int * c = a;

works (compiles without error and is inferred scope)

>
> The above can not be inferred because scope is only inferred 
> when it is assigned
> a limited lifetime. So it is an error.

Rule number 2 of the DIP1000 between quotes

"2. A variable is inferred to be scope if it is initialized with 
a value that has a non-∞ lifetime."

I made an error here. Once scope always scope. And will infer 
scope as much as
possible. Rule two is more for local variables that haven't even 
been marked
with scope. A pointer to them needs to be inferred scope.


>
> ---
> How is a person able to understand this DIP?


./dmd -betterC -dip1000 test.d

> ---
>
> How many DIP manager are there?

I'll assume single person.

> When is a DIP assigned a number?
>
> ---