What advantages do ref params give over pointer params?

struct MyStruct {
	string str;

	this(string str) { this.str = str; }
}

void processRef(ref MyStruct ms) {
	writeln("processRef: ", ms);
}

void processPointer(MyStruct* ms) {
	writeln("processPointer: ", *ms);
}

void main(string[] args) {
	auto ms = MyStruct("the ultimate answer to everythin is the number 42");

	processRef(ms);
	processPointer(&ms);
}

ref2401:

> void processRef(ref MyStruct ms) {
> 	writeln("processRef: ", ms);
> }
>
> void processPointer(MyStruct* ms) {
> 	writeln("processPointer: ", *ms);

ref params don't need the "*" every time you use them inside the function, and don't need the "&" when you call the function.

Bye,
bearophile

processPointer(&ms);
I think doing this way is more descriptive.
Now all readers know that ms might be changed inside the function.

On Friday, 24 April 2015 at 13:39:35 UTC, ref2401 wrote:
> processPointer(&ms);
> I think doing this way is more descriptive.
> Now all readers know that ms might be changed inside the function.

C# avoids that problem requiring (in most cases) the usage of "ref" at the calling point too. But this idea was refused for D (also because it goes against UFCS chains).

Bye,
bearophile

On 4/24/15 9:23 AM, ref2401 wrote:
> What advantages do ref params give over pointer params?
>
> struct MyStruct {
>      string str;
>
>      this(string str) { this.str = str; }
> }
>
> void processRef(ref MyStruct ms) {
>      writeln("processRef: ", ms);
> }
>
> void processPointer(MyStruct* ms) {
>      writeln("processPointer: ", *ms);
> }
>
> void main(string[] args) {
>      auto ms = MyStruct("the ultimate answer to everythin is the number
> 42");
>
>      processRef(ms);
>      processPointer(&ms);
> }

A ref param is somewhat safer, because you cannot do pointer arithmetic on it. A ref will ALWAYS point at the same memory location, because it cannot be rebound.

The compiler can also take advantage of the characteristics of ref, as it does with the -dip25 switch.

-Steve

On 04/24/2015 06:23 AM, ref2401 wrote:

> What advantages do ref params give over pointer params?

Another difference is that a ref parameter is not null and what is referred to is not an rvalue.

However, it is possible to break that expectation if a pointer is dereferenced and passed to a ref-taking function but then the actual object is gone before the reference is used.

Ali

Thank you