in a template argument, specify which object member to access?
object.member lets me access the member of the object, but what
if I want to access those members in a generic way, but in a
different arrangement depending on context? Like if I wanted to
first follow a tree down, and second priority would be going left
to right, but then I wanted to first go right, and second
priority would be going down to up.
struct A {
string up;
string down;
string left;
string right;
}
template goPlaces(D1,D2,D3) {
string go(A a) {
return "go " ~ a.D1 ~ " then go " ~ a.D2 ~ " then go " ~ a.D3;
}
}
import std.stdio;
void main() {
A a = {"north","south","east","west"};
writeln(goPlaces!(up,down,left)(a));
}
Do I just have to use a mixin? Or implement those members as
indexes in an array, if I want to use them differently?
enum Way { UP, DOWN, LEFT, RIGHT };
struct A {
string[Way.max+1] ways;
}
...
Re: in a template argument, specify which object member to access?
This is what I have so far. Using mixin(rawstring~templatearg)
for every time I access the member is kind of cludgy though.
struct A {
string up;
string down;
string left;
string right;
}
template goPlaces(string D1, string D2, string D3) {
string goPlaces(ref A a) {
mixin("a."~D2) = "deetoo";
return "go " ~
mixin("a."~D1) ~ " then go " ~
mixin("a."~D2) ~ " then go " ~
mixin("a."~D3);
}
}
void main() {
import std.stdio;
A a = {"north","south","east","west"};
writeln(goPlaces!("up","left","down")(a));
writeln(a.left);
}
top postinglol
On Monday, 8 February 2016 at 21:09:47 UTC, cy wrote:
object.member lets me access the member of the object, but what
if I want to access those members in a generic way, but in a
different arrangement depending on context? Like if I wanted to
first follow a tree down, and second priority would be going
left to right, but then I wanted to first go right, and second
priority would be going down to up.
struct A {
string up;
string down;
string left;
string right;
}
template goPlaces(D1,D2,D3) {
string go(A a) {
return "go " ~ a.D1 ~ " then go " ~ a.D2 ~ " then go " ~ a.D3;
}
}
import std.stdio;
void main() {
A a = {"north","south","east","west"};
writeln(goPlaces!(up,down,left)(a));
}
Do I just have to use a mixin? Or implement those members as
indexes in an array, if I want to use them differently?
enum Way { UP, DOWN, LEFT, RIGHT };
struct A {
string[Way.max+1] ways;
}
...
Re: in a template argument, specify which object member to access?
On Monday, 8 February 2016 at 22:38:45 UTC, Mengu wrote:
i believe you can use __traits(getMember) there.
Great! Should have refreshed before sending that reply...
I wonder if mixin("a."~member) is better or worse than
__traits(getMember,a,member)...
Re: in a template argument, specify which object member to access?
On Monday, 8 February 2016 at 21:09:47 UTC, cy wrote: object.member lets me access the member of the object, but what if I want to access those members in a generic way, but in a different arrangement depending on context? Like if I wanted to first follow a tree down, and second priority would be going left to right, but then I wanted to first go right, and second priority would be going down to up. [...] i believe you can use __traits(getMember) there.
Re: in a template argument, specify which object member to access?
On Monday, 8 February 2016 at 22:46:06 UTC, cy wrote:
On Monday, 8 February 2016 at 22:38:45 UTC, Mengu wrote:
i believe you can use __traits(getMember) there.
Great! Should have refreshed before sending that reply...
I wonder if mixin("a."~member) is better or worse than
__traits(getMember,a,member)...
i think it's a matter of taste and here's how i would do it:
import std.stdio;
import std.array;
struct A {
string up;
string down;
string left;
string right;
}
string goPlaces(args...)(A a) {
string[] result;
foreach (arg; args) {
result ~= __traits(getMember, a, arg);
}
return "go " ~ result.join(" then go ");
}
void main() {
A a = {"north", "south", "east", "west"};
writeln(goPlaces!("up", "down", "left")(a));
writeln(goPlaces!("down", "right", "left", "up")(a));
}
// outputs
// go north then go south then go east
// go south then go west then go east then go north
Re: in a template argument, specify which object member to access?
On Monday, 8 February 2016 at 22:46:06 UTC, cy wrote:
On Monday, 8 February 2016 at 22:38:45 UTC, Mengu wrote:
i believe you can use __traits(getMember) there.
Great! Should have refreshed before sending that reply...
I wonder if mixin("a."~member) is better or worse than
__traits(getMember,a,member)...
I think I prefer the mixin version because it doesn't rely on
compiler internals and is easier to read IMHO but this is very
questionable.
