• Timothee Cour via Digitalmars-d-learn (14/14) May 21 2015 Can I create an instance of A without calling a constructor? (see below)
• John Colvin (4/23) May 21 2015 For a start I'm pretty sure you want to be calling
• Baz (15/34) May 21 2015 based on this:
• Jacob Carlborg (6/21) May 21 2015 Here's how I do it in my serialization library Orange [1]
• timotheecour (2/30) May 25 2015 Thanks!

Timothee Cour via Digitalmars-d-learn <digitalmars-d-learn puremagic.com> writes:

Can I create an instance of A without calling a constructor? (see below)
Use case: for generic deserialiaztion, when the deserialization library
encounters a class without default constructor for example (it knows what
the fields should be set to, but doesn't know how to construct the object).

class A{
  int x=2;
  this(int x){
    this.x=x;
  }
}


This came up here:
https://github.com/msgpack/msgpack-d/issues/54#issuecomment-104136148
I provide some hacky solution for that in that thread but I suspect it's
not safe and something is missing.

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 21 May 2015 at 09:06:59 UTC, Timothee Cour wrote:
 Can I create an instance of A without calling a constructor? 
 (see below)
 Use case: for generic deserialiaztion, when the deserialization 
 library
 encounters a class without default constructor for example (it 
 knows what
 the fields should be set to, but doesn't know how to construct 
 the object).

 class A{
   int x=2;
   this(int x){
     this.x=x;
   }
 }


 This came up here:
 https://github.com/msgpack/msgpack-d/issues/54#issuecomment-104136148
 I provide some hacky solution for that in that thread but I 
 suspect it's
 not safe and something is missing.

For a start I'm pretty sure you want to be calling 
core.memory.GC.malloc not core.stdc.stdlib.malloc, otherwise you 
leak the memory.

"Baz" <bb.temp gmx.com> writes:

On Thursday, 21 May 2015 at 09:06:59 UTC, Timothee Cour wrote:
 Can I create an instance of A without calling a constructor? 
 (see below)
 Use case: for generic deserialiaztion, when the deserialization 
 library
 encounters a class without default constructor for example (it 
 knows what
 the fields should be set to, but doesn't know how to construct 
 the object).

 class A{
   int x=2;
   this(int x){
     this.x=x;
   }
 }


 This came up here:
 https://github.com/msgpack/msgpack-d/issues/54#issuecomment-104136148
 I provide some hacky solution for that in that thread but I 
 suspect it's
 not safe and something is missing.

based on this:

https://github.com/D-Programming-Language/druntime/blob/6698ee21d4eb00ec2e8c621993359d235618df75/src/rt/lifetime.d#L71

you can create an instance without calling the constructor like 
this:

---
CT construct(CT, A...)(A a)
if (is(CT == class))
{
     auto memory = malloc(typeid(CT).init.length);
     memory[0 .. typeid(CT).init.length] = typeid(CT).init[];
     return cast(CT) memory;
}
---

actually it only copies the fields with their initial values.

Jacob Carlborg <doob me.com> writes:

On 2015-05-21 11:06, Timothee Cour via Digitalmars-d-learn wrote:
 Can I create an instance of A without calling a constructor? (see below)
 Use case: for generic deserialiaztion, when the deserialization library
 encounters a class without default constructor for example (it knows
 what the fields should be set to, but doesn't know how to construct the
 object).

 class A{
    int x=2;
    this(int x){
      this.x=x;
    }
 }


 This came up here:
 https://github.com/msgpack/msgpack-d/issues/54#issuecomment-104136148
 I provide some hacky solution for that in that thread but I suspect it's
 not safe and something is missing.

Here's how I do it in my serialization library Orange [1]

[1] 
https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L166

-- 
/Jacob Carlborg

"timotheecour" <timothee.cour2 gmail.com> writes:

On Thursday, 21 May 2015 at 19:06:35 UTC, Jacob Carlborg wrote:
 On 2015-05-21 11:06, Timothee Cour via Digitalmars-d-learn 
 wrote:
 Can I create an instance of A without calling a constructor? 
 (see below)
 Use case: for generic deserialiaztion, when the 
 deserialization library
 encounters a class without default constructor for example (it 
 knows
 what the fields should be set to, but doesn't know how to 
 construct the
 object).

 class A{
   int x=2;
   this(int x){
     this.x=x;
   }
 }


 This came up here:
 https://github.com/msgpack/msgpack-d/issues/54#issuecomment-104136148
 I provide some hacky solution for that in that thread but I 
 suspect it's
 not safe and something is missing.

 Here's how I do it in my serialization library Orange [1]

 [1] 
 https://github.com/jacob-carlborg/orange/blob/master/orange/util/Reflection.d#L166

Thanks!