www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.dtl - D struct are difficult to work with!

reply Hong Wing <Hong_member pathlink.com> writes:
I found D structs to be harder to work with than C++ ones, for example, with
array i can directly modify a struct by

array[i].x = 9;

but when it is in a Vector, I need to copy it out, modify the copy, and copy
back into the Vector.

SomeStruct s = vector[i];
s.x = 9;
vector[i] = s;

Using a pointer is very inconvenient, especially for math structs, I can see
things like

*result = (*a + *b) * (*c)

Would it be nice to extend "inout" to function return, so to have Vector opIndex
with the following signature for structs:

inout value_type opIndex(index_type index)

This helps to make containers more transparent with native array, and much nicer
to work with. And extend it to variables:

inout SomeStruct s = vector[i];
s.x = 9;
Mar 19 2006
next sibling parent Hasan Aljudy <hasan.aljudy gmail.com> writes:
Hong Wing wrote:
 I found D structs to be harder to work with than C++ ones, for example, with
 array i can directly modify a struct by
 
 array[i].x = 9;
 
 but when it is in a Vector, I need to copy it out, modify the copy, and copy
 back into the Vector.
 
 SomeStruct s = vector[i];
 s.x = 9;
 vector[i] = s;
 
 Using a pointer is very inconvenient, especially for math structs, I can see
 things like
 
 *result = (*a + *b) * (*c)
 
 Would it be nice to extend "inout" to function return, so to have Vector
opIndex
 with the following signature for structs:
 
 inout value_type opIndex(index_type index)
 
 This helps to make containers more transparent with native array, and much
nicer
 to work with. And extend it to variables:
 
 inout SomeStruct s = vector[i];
 s.x = 9;
 
 
 

is there a particular problem with using a class rather than a struct?
Mar 19 2006
prev sibling parent reply Derek Parnell <derek psych.ward> writes:
On Sun, 19 Mar 2006 08:16:26 +0000 (UTC), Hong Wing wrote:

 I found D structs to be harder to work with than C++ ones, for example, with
 array i can directly modify a struct by
 
 array[i].x = 9;
 
 but when it is in a Vector, I need to copy it out, modify the copy, and copy
 back into the Vector.
 
 SomeStruct s = vector[i];
 s.x = 9;
 vector[i] = s;
 
 Using a pointer is very inconvenient, especially for math structs, I can see
 things like
 
 *result = (*a + *b) * (*c)
 
 Would it be nice to extend "inout" to function return, so to have Vector
opIndex
 with the following signature for structs:
 
 inout value_type opIndex(index_type index)
 
 This helps to make containers more transparent with native array, and much
nicer
 to work with. And extend it to variables:
 
 inout SomeStruct s = vector[i];
 s.x = 9;

I'm sorry but I don't know what you are meaning by 'vector' in this context? Do you mean a reference to an array of structs? Can you show me some real code that demonstrates the issue for you. -- Derek (skype: derek.j.parnell) Melbourne, Australia "Down with mediocracy!" 20/03/2006 11:08:55 AM
Mar 19 2006
parent Hong Wing <Hong_member pathlink.com> writes:
Sorry, vector is DTL Vector

struct SomeStruct
{
int x, y, z;
}

Vector!(SomeStruct) vector = new Vector!(SomeStruct)();

to modify entry i, the whole struct needs to be copied from the Vector, modify
the copy, and store the modified copy back into the Vector:

SomeStruct s = vector[i];
vector[i].x = 9;  // does nothing meaningful
s.x = 9;
vector[i] = s;   // changes entry i

This is inconsistent with the behaviour of array, in the case of array, such
copy out, copy in is not needed:

SomeStruct[] array = new SomeStruct[10];
array[i].x = 9;   // changes entry i

For large struct, it is inefficient to copy the whole struct out and copy it
back into the vector

Therefore I propose "inout SomeStruct" as the return type of index operator of
Vector!(SomeStruct), and allow the user to modify the entry directly using the
returned value to achieve array like syntax.

inout SomeStruct opIndex(index_type index)

inout SomeStruct is analogous to inout parameter of function parameters, which
allows a reference to be retrieved from the Vector.

Hong Wing



In article <depxwcj060qq.le9mfgd7onwz$.dlg 40tude.net>, Derek Parnell says...
On Sun, 19 Mar 2006 08:16:26 +0000 (UTC), Hong Wing wrote:

 I found D structs to be harder to work with than C++ ones, for example, with
 array i can directly modify a struct by
 
 array[i].x = 9;
 
 but when it is in a Vector, I need to copy it out, modify the copy, and copy
 back into the Vector.
 
 SomeStruct s = vector[i];
 s.x = 9;
 vector[i] = s;
 
 Using a pointer is very inconvenient, especially for math structs, I can see
 things like
 
 *result = (*a + *b) * (*c)
 
 Would it be nice to extend "inout" to function return, so to have Vector
opIndex
 with the following signature for structs:
 
 inout value_type opIndex(index_type index)
 
 This helps to make containers more transparent with native array, and much
nicer
 to work with. And extend it to variables:
 
 inout SomeStruct s = vector[i];
 s.x = 9;

I'm sorry but I don't know what you are meaning by 'vector' in this context? Do you mean a reference to an array of structs? Can you show me some real code that demonstrates the issue for you. -- Derek (skype: derek.j.parnell) Melbourne, Australia "Down with mediocracy!" 20/03/2006 11:08:55 AM

Mar 19 2006