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digitalmars.D.learn - Complicated property access only works when I write an extra

reply realhet <real_het hotmail.com> writes:
Hello,

I tried to narrow the problem and make a small example, but I've 
failed.

I try to describe the syndrome, maybe someone knows about it.
(I heard that  properties are not 100% functional, maybe it's 
because of that, I dunno...)

With pragma msg, I verify the time of things:

karcSamples
This is a class, I create it from a class template, which has a 
lot of template mixins inside.

karcSamples[key]
The type of this is a RecordAccessor struct, which is a Voldemort 
struct inside a function. That function is called by 
karcSamples.opIndex(key).

karcSamples[key].lod0
The type of this is BlobLoader
'lod0' is a mixin generated  property getter. It calls a template 
function in the karcSamples class: _getBlob!"lod0"(key)  this 
also calls an internal struct called DataLoggerBlobAA which is 
acting like an associative array.  That iternal struct overloads 
the opBinary!"in" operator and returns a BlobLoader struct.

karcSamples[key].lod0._size    ->   _error_     void has no 
property ._size
But this is weird, because BlobLoader actually HAS a  property 
called _size.

karcSamples[key].lod0()
The type of this is also BlobLoader.  I have a feeling, that 
karcSamples[key].lod0 only returns a function pointer (the 
property function) which is implicitly evaluated, except when I 
use the ._size thing to evaluate a property.

karcSamples[key].lod0()._size
And this finally works, but it's ugly.

Anyone knows how to eliminate that extra () from there?  The 
typeof() is works good for it, but the actual compilation thinks 
it's "void", not the BlobLoader struct reported by typeof(). Only 
the extra () let it compile successfuly.
May 26 2023
next sibling parent reply Adam D Ruppe <destructionator gmail.com> writes:
On Friday, 26 May 2023 at 21:00:20 UTC, realhet wrote:

 Only the extra () let it compile successfuly.


No way to fix it. If the function takes an extra argument you can 
kinda trick it but for zero arg function pointer return from a 
property it is just plain broken and has been the whole time.

Don't expect it to ever be fixed.
May 26 2023
parent reply realhet <real_het hotmail.com> writes:
On Friday, 26 May 2023 at 21:11:45 UTC, Adam D Ruppe wrote:

 On Friday, 26 May 2023 at 21:00:20 UTC, realhet wrote:

 Only the extra () let it compile successfuly.


 No way to fix it. If the function takes an extra argument you 
 can kinda trick it but for zero arg function pointer return 
 from a property it is just plain broken and has been the whole 
 time.

 Don't expect it to ever be fixed.


At least my 5 hour trying-and-failing session comes to a logical 
end here :D

Thank You!
May 26 2023
parent realhet <real_het hotmail.com> writes:
It seems like I managed to solve it.

All the chain of properties now capturing a generic value type T.
And finally the most inner associative array will handle the 
implicit cast.
Maybe that extra implicit () got confused when the types are 
same, but the aliases to those types are different. o.O

Now both expressions are working.

    samples[key].mainPicture().width
    samples[key].mainPicture.width

Side effect: The internal chaos behind this also got rediced by 
25% as I had to refactor to find the root of the problem :D
May 27 2023
prev sibling parent realhet <real_het hotmail.com> writes:
On Friday, 26 May 2023 at 21:00:20 UTC, realhet wrote:

Update:
```
auto x = karcSamples[a.key].lod0;	print(x._size);
auto y = karcSamples[a.key].lod0();	print(y._size);
with(karcSamples[a.key].lod0) print(_size);
with(karcSamples[a.key].lod0()) print(_size);
```
When I put it into a temp variable or inside a with(), then both 
form works ok.

Bit when I try to write the whole thing in a single nice 
expression: No property `_size` for the type `void`.

In the documentation I see this:
- For the expression typeof(exp) where exp is an  property 
function, the type is the return type of the function, rather 
than the type of the function.
- For the expression __traits(compiles, exp) where exp is an 
 property function, a further check is made to see if the 
function can be called.

I think this extra step is not always working and by writing an 
extra () or by using a temp variable or a with(), I was able to 
force it.  I only hope there is a workaround that I can implement 
inside my template things, so the business logic could be nice as 
it can be...
May 26 2023