November 25

On Thursday, 25 November 2021 at 08:31:42 UTC, zjh wrote:

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What does scope mean?

scope on a variable with a pointer type means the pointer value will not leave the scope that the variable is declared in.

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Why I don't understand it?

There are many special cases and the documentation isn't very good.

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What's the point?

To prevent memory corruption in @safe code when working with stack variables.

November 25

On Thursday, 25 November 2021 at 13:43:10 UTC, Dennis wrote:

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scope on a variable with a pointer type means the pointer value will not leave the scope that the variable is declared in.

Thank you for your detailed explanation. I understand roughly.
If attribute deduction is available, can the attr be omitted as much as possible?
If we can't omit an attribute, I want sugar sytax to simplify it.
Looking at funcs, attrs all around, as a lover of clean code, I can't bear it.

November 25

On Thursday, 25 November 2021 at 14:16:21 UTC, zjh wrote:

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If attribute deduction is available, can the attr be omitted as much as possible?

Yes

>

Looking at funcs, attrs all around, as a lover of clean code, I can't bear it.

You don't have to use the attributes, it's there for @nogc @safe library code doing low-level memory management. Your applications are free to ignore it most of the time.

Also, 'clean code' is subjective. The alternative to scope parameters that you sometimes see in C libraries is a 'pointer lifetime' section in a documentation comment, which is:

  • inconsistent (varies per library)
  • not verified for correctness (compiler doesn't understand it)
  • more verbose than a single scope keyword

I don't consider that clean.

November 25

On Thursday, 25 November 2021 at 14:40:09 UTC, Dennis wrote:

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I don't consider that clean.

I usually use C++,C++ has no similar scope,C++ has RAII.
It's like the & of C++ versus the ref of d. & is much simpler than ref.
It would be nice if d had some symbols/sugar syntax to simplify these attributes.

November 25

On Thursday, 25 November 2021 at 15:05:55 UTC, zjh wrote:

>

On Thursday, 25 November 2021 at 14:40:09 UTC, Dennis wrote:

>

I don't consider that clean.

I usually use C++,C++ has no similar scope,C++ has RAII.
It's like the & of C++ versus the ref of d. & is much simpler than ref.
It would be nice if d had some symbols/sugar syntax to simplify these attributes.

I wonder what the reason was to choose ref instead of &. Maybe it's kinder to the parser.

November 25

On Wednesday, 24 November 2021 at 23:50:13 UTC, Dennis wrote:

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5 months ago I described an issue with ref return scope parameters:
DIP1000: 'return scope' ambiguity and why you can't make opIndex work
(N.b. in struct member functions, the this keyword is a ref parameter)

[...]

with return ref and return scope, will there also be a return this for the case like the opIndex functions returning something with the lifetime of the containing struct? I don't quite get how it's otherwise fixing it.

November 25

On Thursday, 25 November 2021 at 15:27:20 UTC, Imperatorn wrote:

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On Thursday, 25 November 2021 at 15:05:55 UTC, zjh wrote:

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On Thursday, 25 November 2021 at 14:40:09 UTC, Dennis wrote:

>

I don't consider that clean.

I usually use C++,C++ has no similar scope,C++ has RAII.
It's like the & of C++ versus the ref of d. & is much simpler than ref.
It would be nice if d had some symbols/sugar syntax to simplify these attributes.

I wonder what the reason was to choose ref instead of &. Maybe it's kinder to the parser.

If you are new to D and don't already know C++, int& will mean nothing to you, whereas you have at least a chance of guessing what ref int means just from reading it.

November 25

On Thursday, 25 November 2021 at 15:59:41 UTC, Paul Backus wrote:

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On Thursday, 25 November 2021 at 15:27:20 UTC, Imperatorn wrote:

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On Thursday, 25 November 2021 at 15:05:55 UTC, zjh wrote:

>

On Thursday, 25 November 2021 at 14:40:09 UTC, Dennis wrote:

>

I don't consider that clean.

I usually use C++,C++ has no similar scope,C++ has RAII.
It's like the & of C++ versus the ref of d. & is much simpler than ref.
It would be nice if d had some symbols/sugar syntax to simplify these attributes.

I wonder what the reason was to choose ref instead of &. Maybe it's kinder to the parser.

If you are new to D and don't already know C++, int& will mean nothing to you, whereas you have at least a chance of guessing what ref int means just from reading it.

So it was more of a readability thing then

November 25

On Thursday, 25 November 2021 at 16:05:01 UTC, Imperatorn wrote:

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On Thursday, 25 November 2021 at 15:59:41 UTC, Paul Backus wrote:

>

If you are new to D and don't already know C++, int& will mean nothing to you, whereas you have at least a chance of guessing what ref int means just from reading it.

So it was more of a readability thing then

I'm only guessing, but I suspect it's a combination of (a) readability, and (b) consistency with other storage classes (which are all words, not punctuation).

November 25

On Thursday, 25 November 2021 at 15:57:13 UTC, WebFreak001 wrote:

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with return ref and return scope, will there also be a return this for the case like the opIndex functions returning something with the lifetime of the containing struct? I don't quite get how it's otherwise fixing it.

return this in struct member functions is return ref. Walter proposes in the bugzilla issue to allow ref after the parameter list:

struct S {
    ref int opIndex() return ref scope {

    }
}
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