• ref2401 (6/6) May 15 2015 What is the difference between 'const' and 'in' parameter storage
• Adam D. Ruppe (7/7) May 15 2015 The scope storage class means you promise not to escape any
• ref2401 (18/25) May 15 2015 I expected the compiler forbids 'in' params escaping.
• Adam D. Ruppe (2/3) May 15 2015 No, but the compiler check isn't implemented.
• Steven Schveighoffer (3/7) May 15 2015 scope ref const
• ref2401 (3/13) May 15 2015 still getting the error: Error: scope cannot be ref or out
• Steven Schveighoffer (10/22) May 18 2015 interesting. Seems you would be right then.
• Marco Leise (6/34) May 18 2015 Issue 8121 - "scope ref" is perfectly OK

"ref2401" <refactor24 gmail.com> writes:

What is the difference between 'const' and 'in' parameter storage 
classes?
When should I use 'const' or 'in'?

The documentation says 'in' is the same as 'const scope' but I 
can't write 'const scope ref' though it's legal to write 'in ref'.

Thank you

"Adam D. Ruppe" <destructionator gmail.com> writes:

The scope storage class means you promise not to escape any 
reference to the data. This isn't enforced but it is similar in 
concept to Rust's borrowed pointers - it may someday be 
implemented to be an error to store them in an outside variable.

Only use 'in' if you are looking at the data, but not modifying 
or storing copies of pointers/references to it anywhere in any 
way.

"ref2401" <refactor24 gmail.com> writes:

On Friday, 15 May 2015 at 16:08:31 UTC, Adam D. Ruppe wrote:
 The scope storage class means you promise not to escape any 
 reference to the data. This isn't enforced but it is similar in 
 concept to Rust's borrowed pointers - it may someday be 
 implemented to be an error to store them in an outside variable.

 Only use 'in' if you are looking at the data, but not modifying 
 or storing copies of pointers/references to it anywhere in any 
 way.

I expected the compiler forbids 'in' params escaping.

struct MyStruct {
	this(int a) {
		this.a = a;
	}

	int a;
}


const(MyStruct)* globalPtr;

void main(string[] args) {
	MyStruct ms = MyStruct(10);

	foo(ms);
	ms.a = 12;

	writeln("global: ", *globalPtr); // prints const(MyStruct)(12)
}

void foo(in ref MyStruct ms) {
	globalPtr = &ms; // is it legal?
}

"Adam D. Ruppe" <destructionator gmail.com> writes:

On Friday, 15 May 2015 at 18:18:13 UTC, ref2401 wrote:
 	globalPtr = &ms; // is it legal?

No, but the compiler check isn't implemented.

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 5/15/15 12:04 PM, ref2401 wrote:
 What is the difference between 'const' and 'in' parameter storage classes?
 When should I use 'const' or 'in'?

 The documentation says 'in' is the same as 'const scope' but I can't
 write 'const scope ref' though it's legal to write 'in ref'.

scope ref const

-Steve

"ref2401" <refactor24 gmail.com> writes:

On Friday, 15 May 2015 at 16:30:29 UTC, Steven Schveighoffer 
wrote:
 On 5/15/15 12:04 PM, ref2401 wrote:
 What is the difference between 'const' and 'in' parameter 
 storage classes?
 When should I use 'const' or 'in'?

 The documentation says 'in' is the same as 'const scope' but I 
 can't
 write 'const scope ref' though it's legal to write 'in ref'.

 scope ref const

 -Steve

still getting the error: Error: scope cannot be ref or out

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 5/15/15 2:19 PM, ref2401 wrote:
 On Friday, 15 May 2015 at 16:30:29 UTC, Steven Schveighoffer wrote:
 On 5/15/15 12:04 PM, ref2401 wrote:
 What is the difference between 'const' and 'in' parameter storage
 classes?
 When should I use 'const' or 'in'?

 The documentation says 'in' is the same as 'const scope' but I can't
 write 'const scope ref' though it's legal to write 'in ref'.

 scope ref const

 still getting the error: Error: scope cannot be ref or out

interesting. Seems you would be right then.

The only other possibility could be ref scope const, but that doesn't 
seem right, I'll try it.

Nope, so basically there is no way to do in by expanding to scope const. 
This is something that should be considered if we ever want to modify 
what 'in' means.

I am not sure yet whether "in ref" should be valid or "scope ref" should 
be valid either. It doesn't seem to me that it should trigger an error.

-Steve

Marco Leise <Marco.Leise gmx.de> writes:

Am Mon, 18 May 2015 09:05:51 -0400
schrieb Steven Schveighoffer <schveiguy yahoo.com>:

 On 5/15/15 2:19 PM, ref2401 wrote:
 On Friday, 15 May 2015 at 16:30:29 UTC, Steven Schveighoffer wrote:
 On 5/15/15 12:04 PM, ref2401 wrote:
 What is the difference between 'const' and 'in' parameter storage
 classes?
 When should I use 'const' or 'in'?

 The documentation says 'in' is the same as 'const scope' but I can't
 write 'const scope ref' though it's legal to write 'in ref'.

 scope ref const

 still getting the error: Error: scope cannot be ref or out

 
 interesting. Seems you would be right then.
 
 The only other possibility could be ref scope const, but that doesn't 
 seem right, I'll try it.
 
 Nope, so basically there is no way to do in by expanding to scope const. 
 This is something that should be considered if we ever want to modify 
 what 'in' means.
 
 I am not sure yet whether "in ref" should be valid or "scope ref" should 
 be valid either. It doesn't seem to me that it should trigger an error.
 
 -Steve

Issue 8121 - "scope ref" is perfectly OK
https://issues.dlang.org/show_bug.cgi?id=8121

-- 
Marco