Re: OpIndex/OpIndexAssign strange order of execution
void main() {
auto s = S();
s["b", "c"] = s["a"];
}
Prints
a
["b", "c"]
Ali
I thought about this too, thanks!
Re: OpIndex/OpIndexAssign strange order of execution
Have you considered the multiple indexes?
https://dlang.org/spec/operatoroverloading.html#index_assignment_operator
It may give you some power in execution order.
import std.stdio;
struct S {
auto opIndex(string index) {
writeln(index);
return 42;
}
auto opIndexAssign(int value, string[] indexes...) {
writeln(indexes);
}
}
void main() {
auto s = S();
s["b", "c"] = s["a"];
}
Prints
a
["b", "c"]
Ali
Re: OpIndex/OpIndexAssign strange order of execution
On Monday, 18 September 2017 at 15:14:20 UTC, Moritz Maxeiner
wrote:
On Monday, 18 September 2017 at 15:11:34 UTC, Moritz Maxeiner
wrote:
gets rewritten to
---
t.opIndex("b").opIndexAssign(t["a"].value, "c");
---
Sorry, forgot one level of rewriting:
---
t.opIndex("b").opIndexAssign(t.opIndex("a").value, "c");
---
Nice, thanks for the explanation :)
This will be a problem for me because in my use case the internal
operations of the structs are stack-like manipulations.
So in this case
t["b"]["c"] = t["a"].value;
instead of manipulating the internal stack with "a" then "b" and
"c" I got this weird order of "b", "a", "c" messing with the
internal stack logic.
Well, back to work :)
Re: OpIndex/OpIndexAssign strange order of execution
On Monday, 18 September 2017 at 15:11:34 UTC, Moritz Maxeiner
wrote:
gets rewritten to
---
t.opIndex("b").opIndexAssign(t["a"].value, "c");
---
Sorry, forgot one level of rewriting:
---
t.opIndex("b").opIndexAssign(t.opIndex("a").value, "c");
---
Re: OpIndex/OpIndexAssign strange order of execution
On Sunday, 17 September 2017 at 18:52:39 UTC, SrMordred wrote:
struct Test{ [...] }
Test t;
As described in the spec [1]
t["a"] = 100;
gets rewritten to
---
t.opIndexAssign(100, "a");
---
, while
t["b"]["c"] = t["a"].value;
gets rewritten to
---
t.opIndex("b").opIndexAssign(t["a"].value, "c");
---
, which has to result in your observed output (left-to-right
evaluation order):
//OUTPUT:
opIndexAssign : index : a , value : 100
opIndex : index : b
opIndex : index : a
property value : 100
opIndexAssign : index : c , value : 100
//EXPECTED OUTPUT
opIndexAssign : index : a , value : 100
opIndex : index : a
property value : 100
opIndex : index : b
opIndexAssign : index : c , value : 100
Is this right?
AFAICT from the spec, yes. Your expected output does not match
D's rewriting rules for operator overloading.
I find unexpected this mix of operations on left and right side
of an equal operator.
Adding some more examples to the spec to show the results of the
rewriting rules could be useful, but AFAICT it's unambiguous.
On Monday, 18 September 2017 at 13:38:48 UTC, SrMordred wrote:
Should I report this as a bug?
Not AFAICT.
I tried a C++ equivalent code and it execute in the expected
order.
D does not (in general) match C++ semantics.
[1] https://dlang.org/spec/operatoroverloading.html
Re: OpIndex/OpIndexAssign strange order of execution
Should I report this as a bug? I tried a C++ equivalent code and it execute in the expected order.
OpIndex/OpIndexAssign strange order of execution
struct Test{
@property int value(){
writeln("property value : ", _value);
return _value;
}
int _value;
Test opIndex( string index )
{
writeln( "opIndex : index : ", index );
return this;
}
Test opIndexAssign(int value, string index )
{
writeln( "opIndexAssign : value : ", value, " , index :
", index );
this._value = value;
return this;
}
}
Test t;
t["a"] = 100;
t["b"]["c"] = t["a"].value;
//OUTPUT:
opIndexAssign : index : a , value : 100
opIndex : index : b
opIndex : index : a
property value : 100
opIndexAssign : index : c , value : 100
//EXPECTED OUTPUT
opIndexAssign : index : a , value : 100
opIndex : index : a
property value : 100
opIndex : index : b
opIndexAssign : index : c , value : 100
Is this right?
I find unexpected this mix of operations on left and right side
of an equal operator.
