How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
I want to make a custom dictionary that I may iterate through
with foreach. Several times.
What I observe so far is that my dict as a simple forward range
is exhausted after the first foreach and I have to deeply copy it
beforehand.
With a simple associative array the exhaustion is not observed.
Is there a (hopefully simple) way to make this
automatic/transparent? Of course
I need to use the struct.
Can I add a save member function? If yes: How? Or is there an
operator that is used in the foreach initialization that I may
overload in this struct?
My code:
```d
import std.stdio;
import std.string;
import std.typecons;
struct mydict {
string[string] dct;
@property bool empty() const {
return dct.empty;
}
@property ref auto front() {
return tuple(dct.keys[0], dct[dct.keys[0]]);
}
void popFront() {
dct.remove(dct.keys[0]);
}
void opAssign(mydict rhs) {
writeln("--opAssign--");
foreach (k; rhs.dct.keys) // do a deep copy
dct[k] = rhs.dct[k];
}
}
void main() {
mydict md, md2;
md.dct = ["h":"no", "d":"ex", "r": "cow"];
md2 = md; // md2.opAssign(md)
foreach (k, v; md)
writeln("key: ", k, "val: ", v);
writeln("--");
foreach (k, v; md) // does not work with md again, md is
exhausted
writeln("key: ", k, "val: ", v);
}
```
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Wednesday, 13 March 2024 at 22:16:52 UTC, rkompass wrote:
I want to make a custom dictionary that I may iterate through
with foreach. Several times.
What I observe so far is that my dict as a simple forward range
is exhausted after the first foreach and I have to deeply copy
it beforehand.
With a simple associative array the exhaustion is not observed.
Is there a (hopefully simple) way to make this
automatic/transparent? Of course
I need to use the struct.
Can I add a save member function? If yes: How? Or is there an
operator that is used in the foreach initialization that I may
overload in this struct?
you need to seperate the range state from the data
```d
import std;
auto tuple(T...)(T t){
struct tuple{
T me; alias me this;
}
return tuple(t);
}
struct mydict(T,S){
T[S] dct;
void opAssign(mydict rhs) {
writeln("--opAssign--");
foreach (k; rhs.dct.keys) // do a deep copy
dct[k] = rhs.dct[k];
}
auto opSlice(){
struct range{
T[S]* parent;
int i;
auto front()=>
tuple(parent.keys[i],(*parent)[parent.keys[i]]);
auto popFront()=>i++;
auto empty()=>parent.keys.length<=i;
}
return range(&this.dct);
}
}
void main() {
mydict!(string,string) md, md2;
md.dct = ["h":"no", "d":"ex", "r": "cow"];
md2 = md; // md2.opAssign(md)
foreach (k, v; md[])
writeln("key: ", k, "val: ", v);
writeln("--");
foreach (k, v; md[]) // does not work with md again, md is
exhausted
writeln("key: ", k, "val: ", v);
}
```
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
Hello @monkyyy,
thank you for your help. I will study and try your code.
Meanwhile I have found that I can add this function into the
struct:
```d
// postblit constructor, see
//
https://stackoverflow.com/questions/38785624/d-struct-copy-constructor
this(this) {
string[string] ndct;
foreach (k; dct.keys) // do a deep copy
ndct[k] = dct[k];
dct = ndct;
}
```
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Thursday, 14 March 2024 at 16:32:10 UTC, rkompass wrote: On Thursday, 14 March 2024 at 16:12:00 UTC, rkompass wrote: Hello @monkyyy again, your solution is much more elegant:-) No need to do a deep copy. I was thinking about a way to achieve that but had no clue. I will study opSlice now. Your definition of tuple is somewhat obscure to me. Is this compatible with the Tuple from `std.typecons`? Greetings, Raul Std.tuple is a gaint mess if there's differences in usage syntax they are very stupid tradeoffs; fundementally the base languge has allot of syntax sugar for "aliasSeq" and my definition of tuple is sticking an Seq into a struct; if you look at the code for std.tuple it will do the same thing under the name "expand" If you go down the rabbit hole of learning the template syntax you should start with the systax aviable for seq's and 95% of it will apply to that definition of tuple
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
@Monkyyy: I adopted your solution, it is perfect. I only have one problem left: The foreach loop with associative arrays has two cases: `foreach(key, val; arr)` and `foreach(x; arr)`. In the second case only the values are iterated. With the present solution the iteration delivers (key, val) tuples. Can this somehow be detected by the opSlice or is there another overloading construct to be applied for this? Addition: I noted that in the best matching [docs](https://dlang.org/spec/operatoroverloading.html#slice) only *ordinary arrays* are covered. Your solution would make a very nice addition for the case of associative arrays there. I learn't a lot from it. Should I do an improvement request somewhere?
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Friday, 15 March 2024 at 09:03:25 UTC, rkompass wrote:
@Monkyyy: I adopted your solution, it is perfect.
I only have one problem left:
The foreach loop with associative arrays has two cases:
`foreach(key, val; arr)` and `foreach(x; arr)`.
In the second case only the values are iterated.
With the present solution the iteration delivers (key, val)
tuples.
That will not be fixed in d2 ranges and has no good solutions;
and my affect over d3 seems to be none. You could ask around for
the "opApply" solution but I dont know it well (and prefer ranges)
d2 Ranges are based on a simplification of stl's ideas and stl
doesn't support arrays-like iteration well, I wish to change that
and working on a proof of concept algorthims lib... but well,
this is unlikely to work.
For d3 if changing the range interface fails, expect to see style
guides say "prefer explict range starters" string.byUnicode and
string.byAscii will probably be how they kill `autodecoding` and
your data stucture having 2 range functions as `byKey` and
`byKeyValue` will look the same.
Should I do an improvement request somewhere?
I think its been kinda of piecemeal and D1 1D(repetition
intentional) opSlice is in limbo(it was deprecated, and then
slightly undepercated in some random chats, its a mess)
for completeness I believe the current state of 1d op overloads
are:
opIndex(int)
opIndex(key)
opSlice()
opSlice(int, int)
int opDollar()
dollar opDollar()
opSlice(int, dollar)
opBinararyRight("in",K)(key) (opIn was deprecated and shouldn't
have been)
If your confident in your writing ability id suggest a clean
slate article based on this list and what the compiler actually
does(maybe ask around for any I missed) rather than trying to
untangle this mess
Or write a dip thread "undeperacate d1 opOverloads that are still
wanted by everyone") and try to bring back opIn at the same time
and get the limboness of old technically deprecated 1d array
opOverloads officially gone
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Friday, 15 March 2024 at 17:15:56 UTC, monkyyy wrote:
On Friday, 15 March 2024 at 09:03:25 UTC, rkompass wrote:
@Monkyyy: I adopted your solution, it is perfect.
I only have one problem left:
The foreach loop with associative arrays has two cases:
`foreach(key, val; arr)` and `foreach(x; arr)`.
In the second case only the values are iterated.
With the present solution the iteration delivers (key, val)
tuples.
That will not be fixed in d2 ranges and has no good solutions;
and my affect over d3 seems to be none. You could ask around
for the "opApply" solution but I dont know it well (and prefer
ranges)
d2 Ranges are based on a simplification of stl's ideas and stl
doesn't support arrays-like iteration well, I wish to change
that and working on a proof of concept algorthims lib... but
well, this is unlikely to work.
For d3 if changing the range interface fails, expect to see
style guides say "prefer explict range starters"
string.byUnicode and string.byAscii will probably be how they
kill `autodecoding` and your data stucture having 2 range
functions as `byKey` and `byKeyValue` will look the same.
Should I do an improvement request somewhere?
I think its been kinda of piecemeal and D1 1D(repetition
intentional) opSlice is in limbo(it was deprecated, and then
slightly undepercated in some random chats, its a mess)
for completeness I believe the current state of 1d op overloads
are:
opIndex(int)
opIndex(key)
opSlice()
opSlice(int, int)
int opDollar()
dollar opDollar()
opSlice(int, dollar)
opBinararyRight("in",K)(key) (opIn was deprecated and shouldn't
have been)
If your confident in your writing ability id suggest a clean
slate article based on this list and what the compiler actually
does(maybe ask around for any I missed) rather than trying to
untangle this mess
Or write a dip thread "undeperacate d1 opOverloads that are
still wanted by everyone") and try to bring back opIn at the
same time and get the limboness of old technically deprecated
1d array opOverloads officially gone
I'm quite new to D yet. But I have some acquaintance with Python.
Therefore, together with templates the discovery of the Variant
type was inspiring me to the following:
I wanted to explore if it's possible to do sort of type-agnostic
programming with D. This could perhaps enable a simpler
translation of Python code to D.
Trying with a `Variant[Variant] dct;` dictionary I observed that
even simple assignment of key:value pairs was not possible as the
different types are not automatically cast to a Variant.
Embedded in a struct with templating and casts to Variant such a
dict now seems possible:
The preliminary code:
```d
// implement .get .update .require
import std.stdio;
import std.typecons;
import std.range;
import std.variant;
import std.string;
import std.format;
struct dict
{
Variant[Variant] dct;
Variant opIndex(T)(T key) {
return dct[cast(Variant) key];
}
void opIndexAssign(V, T)(V val, T key) {
dct[cast(Variant) key] = cast(Variant) val;
}
auto opBinaryRight(string op : "in", T)(T lhs) {
return cast(Variant)lhs in dct;
}
@property auto keys() {
return dct.keys;
}
@property auto values() {
return dct.values;
}
auto remove(T)(T key) {
return dct.remove(cast(Variant) key);
}
@property auto dup() {
dict newd;
foreach (k; dct.keys) // do a deep copy
newd.dct[k] = dct[k];
return newd;
}
void toString(scope void delegate(const(char)[]) sink,
FormatSpec!char fmt) {
put(sink, "dict([");
bool rep = false;
foreach (k; dct.keys) {
if (rep)
put(sink, ", ");
formatValue(sink, k, fmt);
put(sink, ":");
formatValue(sink, dct[k], fmt);
rep = true;
}
put(sink, "])");
}
auto opSlice(){
struct range{
Variant[Variant]* parent;
int i;
auto front()=>
tuple(parent.keys[i],(*parent)[parent.keys[i]]);
auto popFront()=>i++;
auto empty()=>parent.keys.length<=i;
}
return range(&this.dct);
}
}
void main() {
dict d;
writeln("d: ", d);// ==> dict([])
writeln("d.keys: ", d.keys);
writeln("d.values: ", d.values);
writeln("d.keys.length: ", d.keys.length);
writeln("");
writeln("populating dict ");
d["hello"] = 2;
d[3.1] = 5;
d['c'] = 3.14;
d[2] = "freak";
d["mykey"] =
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Friday, 15 March 2024 at 20:36:56 UTC, rkompass wrote: I'm quite new to D yet. But I have some acquaintance with Python. Therefore, together with templates the discovery of the Variant type was inspiring me to the following: I wanted to explore if it's possible to do sort of type-agnostic programming with D. This could perhaps enable a simpler translation of Python code to D. Trying with a `Variant[Variant] dct;` dictionary I observed that even simple assignment of key:value pairs was not possible as the different types are not automatically cast to a Variant. You're not the first one. There's no technical reason for the restriction. It's simply a matter of being opposed by those who make these decisions on the basis that it's the wrong way to program or something like that. Here is a recent thread: https://forum.dlang.org/post/ikwphfwevgnsxmdfq...@forum.dlang.org
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Friday, 15 March 2024 at 20:36:56 UTC, rkompass wrote: I start to see that D is heavily influenced by C++ (STL), not just C. This is not bad It is just bad; ranges are not pairs of 2 pointers, stepov was comprising with c++ or if he thinks c++ iterators are objectively good(not good for making something work with c++) he's lacks taste even simplified a "random access range" is to complex an api(close to 20 functions) when Im pretty sure you need 6 functions for a coherent array-like interface and when your talking about 100 algorthims, well 1400 functions matters
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
To solve the problem with the 1-variable and 2-variable versions
of foreach I
tried opApply and found that the compiler prefers it over opSlice
and opIndex() (the latter without argument).
My code:
```d
int opApply(int delegate(Variant) foreachblock) const {
int result = 0;
foreach(val; dct) {
result = foreachblock(val);
if (result)
break;
}
return result;
}
int opApply(int delegate(Variant, Variant) foreachblock) const {
int result = 0;
foreach(key, val; dct) {
result = foreachblock(key, val);
if (result)
break;
}
return result;
}
```
So I'm fine with this now.
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
@bachmeier
You're not the first one. There's no technical reason for the
restriction. It's simply a matter of being opposed by those who
make these decisions on the basis that it's the wrong way to
program or something like that. Here is a recent thread:
https://forum.dlang.org/post/ikwphfwevgnsxmdfq...@forum.dlang.org
Thank you for this. Very interesting discussion. And apparently a
deliberate restriction of flexibility in type conversion.
I will first try to understand better how templates work under
the hood before joining this discussion.
Given the types S and T in say `templfunc(S, T)(S arg1, T arg2)
{}`
represent 2 different actual types in the program, does that mean
that there are 4 versions of the `templfunc` function compiled
in? (This was the C++ way iirc).
Or are the types T and S are put on the stack like ordinary
arguments and the usage of arg1 and arg2 within the function is
enveloped in switches that query these Types?
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Monday, 18 March 2024 at 08:50:42 UTC, rkompass wrote:
Given the types S and T in say `templfunc(S, T)(S arg1, T arg2)
{}`
represent 2 different actual types in the program, does that
mean that there are 4 versions of the `templfunc` function
compiled in? (This was the C++ way iirc).
IMHO, only if you instantiate (make call) templfunc with all
types.
Or are the types T and S are put on the stack like ordinary
arguments and the usage of arg1 and arg2 within the function is
enveloped in switches that query these Types?
IMHO, only if you instantiate (make call) templfunc, then
compiler create function with specified types.
Function created only once for given types combination.
Re: How to make a struct containing an associative array to deeply copy (for repeated usage in foreach) ?
On Monday, 18 March 2024 at 10:05:43 UTC, novice2 wrote: On Monday, 18 March 2024 at 08:50:42 UTC, rkompass wrote: Or are the types T and S are put on the stack like ordinary arguments and the usage of arg1 and arg2 within the function is enveloped in switches that query these Types? IMHO, only if you instantiate (make call) templfunc, then compiler create function with specified types. Function created only once for given types combination. this also can be helpfull: https://dlang.org/spec/template.html#common_instantiation
