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digitalmars.D.learn - Avoiding GC in D and code consistancy

reply Tim Hsu <tim37021 gmail.com> writes:
I came from C++ looking forward to D. Some languages require 
programmers to use GC all the time. However, A lot of time we 
don't really need GC especially when the time of destruction is 
deterministic in compile time.

I found that struct in D is allocate on stack by default. And we 
can use scope! to allocate class on stack too.

See the following code. Struct version of Vector3f can't derive 
toString method. writeln() prints unformated struct members. I 
know I can use helper function here. But is there any other way?

struct Vector3f {
public:
     this(float x, float y, float z) {
         this.x = x;
         this.y = y;
         this.z = z;
     }

      property float length2() {
         return x*x+y*y+z*z;
     }

      property float length() {
         import std.math;
         return sqrt(x*x+y*y+z*z);
     }

     Vector3f opBinary(string op)(Vector3f rhs)
     {
         static if (op == "+") return Vector3f(x+rhs.x, y+rhs.y, 
z+rhs.z);
         else static if (op == "-") return Vector3f(x-rhs.x, 
y-rhs.y, z-rhs.z);
         else static assert(0, "Operator "~op~" not implemented");
     }

     float x, y, z;
}

class version of Vector3f. Require new operator in opBinary(). 
scoped! won't work here.

Is there a better to write vector3f class while avoiding GC?
Dec 30 2017
next sibling parent reply =?UTF-8?Q?Ali_=c3=87ehreli?= <acehreli yahoo.com> writes:
On 12/30/2017 11:16 PM, Tim Hsu wrote:


 Struct version of Vector3f can't derive toString
 method. writeln() prints unformated struct members. I know I can use
 helper function here. But is there any other way?


The normal way that I know is to insert a function like the following 
into Vector3f:

     string toString() {
         import std.string : format;
         return format("%s,%s,%s", x, y, z);
     }


 class version of Vector3f. Require new operator in opBinary(). scoped!
 won't work here.

 Is there a better to write vector3f class while avoiding GC?


Yeah, it doesn't make sense that a type of x, y, z should be a class. I 
would stay with a struct here.

Ali
Dec 30 2017
parent reply Tim Hsu <tim37021 gmail.com> writes:
On Sunday, 31 December 2017 at 07:32:50 UTC, Ali Çehreli wrote:

 On 12/30/2017 11:16 PM, Tim Hsu wrote:


 Struct version of Vector3f can't derive toString
 method. writeln() prints unformated struct members. I know I


 can use

 helper function here. But is there any other way?


 The normal way that I know is to insert a function like the 
 following into Vector3f:

     string toString() {
         import std.string : format;
         return format("%s,%s,%s", x, y, z);
     }


 class version of Vector3f. Require new operator in


 opBinary(). scoped!

 won't work here.

 Is there a better to write vector3f class while avoiding GC?


 Yeah, it doesn't make sense that a type of x, y, z should be a 
 class. I would stay with a struct here.

 Ali


Sorry I am a bit disappointed. It seems writeln itself will check 
if the struct to be printed has toString. If not, it use default 
struct printer.
Dec 31 2017
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 12/31/17 6:16 AM, Tim Hsu wrote:

 On Sunday, 31 December 2017 at 07:32:50 UTC, Ali Çehreli wrote:

 On 12/30/2017 11:16 PM, Tim Hsu wrote:


 Struct version of Vector3f can't derive toString
 method. writeln() prints unformated struct members. I know I


 can use

 helper function here. But is there any other way?


 The normal way that I know is to insert a function like the following 
 into Vector3f:

     string toString() {
         import std.string : format;
         return format("%s,%s,%s", x, y, z);
     }


 class version of Vector3f. Require new operator in


 opBinary(). scoped!

 won't work here.

 Is there a better to write vector3f class while avoiding GC?


 Yeah, it doesn't make sense that a type of x, y, z should be a class. 
 I would stay with a struct here.


 
 Sorry I am a bit disappointed. It seems writeln itself will check if the 
 struct to be printed has toString. If not, it use default struct printer.


Note, you can use a "sink" version of toString as well, and avoid the gc:

void toString(void delegate(const(char)[]) sink)  nogc
{
     // use formatValue to push into the sink
}

-Steve
Dec 31 2017
parent Steven Schveighoffer <schveiguy yahoo.com> writes:
On 12/31/17 7:50 AM, Steven Schveighoffer wrote:


 Note, you can use a "sink" version of toString as well, and avoid the gc:
 
 void toString(void delegate(const(char)[]) sink)  nogc
 {
      // use formatValue to push into the sink
 }


I guess I'm missing some parameters here, go with what Seb linked to :)

-Steve
Dec 31 2017
prev sibling parent Seb <seb wilzba.ch> writes:
On Sunday, 31 December 2017 at 07:16:46 UTC, Tim Hsu wrote:

 I came from C++ looking forward to D. Some languages require 
 programmers to use GC all the time. However, A lot of time we 
 don't really need GC especially when the time of destruction is 
 deterministic in compile time.

 [...]


You can use a custom toString method which doesn't do any 
allocations:

https://wiki.dlang.org/Defining_custom_print_format_specifiers

However, the building blocks (formattedWrite and writeln) aren't 
" nogc" at the moment.
Dec 31 2017