digitalmars.D.learn - alias this/opGet and opCast conversion
This i probably a rather dumb question but I've been up all night
and therefor have a really good excuse ;) (I can barely see
straight...)
Is opGet the reverse opAssign? I can't find any docs on it but it
does let me write converters from my type to another type.
e.g.,
struct X { int value; }
double x = xX;
without an opGet or alias this I get an error about not being
able to implicitly convert. Using alias this solves the problem.
Using opGet seems to let me write a converter(which I can't seem
to do otherwise).
For example, it seems I could use opGet to normalize X's value
when converting to a double.
That is, the way I see it is
double x = xX;
The compiler checks to see if double has an opAssign that will
convert X to a double. If not it checks if X has an opGet call(a
sort of reverse opAssign).
Is this the correct understanding of opGet or is there more too
it.
What if I have
struct X { int value; X opAssign(Y y); }
struct Y { double value; X opGet(); alias opGet this; }
then
X x; Y y;
what does
x = y;
y = x;
do?
It seems the first will call X's opAssign and Y's opGet unless
there is precedence? y = x will fail with the implicit
conversion error?
Dec 17 2012
On Monday, 17 December 2012 at 15:10:24 UTC, js.mdnq wrote:This i probably a rather dumb question but I've been up all night and therefor have a really good excuse ;) (I can barely see straight...) Is opGet the reverse opAssign? I can't find any docs on it but it does let me write converters from my type to another type. e.g., struct X { int value; } double x = xX; without an opGet or alias this I get an error about not being able to implicitly convert. Using alias this solves the problem. Using opGet seems to let me write a converter(which I can't seem to do otherwise). For example, it seems I could use opGet to normalize X's value when converting to a double. That is, the way I see it is double x = xX; The compiler checks to see if double has an opAssign that will convert X to a double. If not it checks if X has an opGet call(a sort of reverse opAssign). Is this the correct understanding of opGet or is there more too it. What if I have struct X { int value; X opAssign(Y y); } struct Y { double value; X opGet(); alias opGet this; }"opGet" is not a special name. The magic comes from alias this. You can use another name just fine.then X x; Y y; what does x = y; y = x; do? It seems the first will call X's opAssign and Y's opGet unless there is precedence?I guess opAssign wins, because alias this is only considered if it doesn't work out with the original type.y = x will fail with the implicit conversion error?Yes, assigning x directly to y doesn't work, and assigning it to y.opGet (via alias this) doesn't work either, so it fails.
Dec 17 2012
"js.mdnq" <js_adddot+mdng gmail.com> On Monday, 17 December 2012 at 15:46:22 UTC, anonymous wrote:On Monday, 17 December 2012 at 15:10:24 UTC, js.mdnq wrote:Thanks, that makes sense... no wonder I couldn't find it.This i probably a rather dumb question but I've been up all night and therefor have a really good excuse ;) (I can barely see straight...) Is opGet the reverse opAssign? I can't find any docs on it but it does let me write converters from my type to another type. e.g., struct X { int value; } double x = xX; without an opGet or alias this I get an error about not being able to implicitly convert. Using alias this solves the problem. Using opGet seems to let me write a converter(which I can't seem to do otherwise). For example, it seems I could use opGet to normalize X's value when converting to a double. That is, the way I see it is double x = xX; The compiler checks to see if double has an opAssign that will convert X to a double. If not it checks if X has an opGet call(a sort of reverse opAssign). Is this the correct understanding of opGet or is there more too it. What if I have struct X { int value; X opAssign(Y y); } struct Y { double value; X opGet(); alias opGet this; }"opGet" is not a special name. The magic comes from alias this. You can use another name just fine.That might be ok because chances are X will not have an opAssign for Y anyways as long as opGet is not called first. Hence opGet should only be called which is what I want. I guess the real problem is that if X does know about Y and has an opAssign for it then there is trouble because opAssign might not convert the value the way I want it to(which is why I'm using opGet).then X x; Y y; what does x = y; y = x; do? It seems the first will call X's opAssign and Y's opGet unless there is precedence?I guess opAssign wins, because alias this is only considered if it doesn't work out with the original type.Thanksy = x will fail with the implicit conversion error?Yes, assigning x directly to y doesn't work, and assigning it to y.opGet (via alias this) doesn't work either, so it fails.
Dec 17 2012