[Issue 16662] Can't call std.variant.visit from a pure function

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

Iain Buclaw  changed:

   What|Removed |Added

   Priority|P1  |P3

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[Issue 16662] Can't call std.variant.visit from a pure function

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

--- Comment #3 from Paul Backus  ---
I've made some progress on this, but am unable to make VariantN.peek pure,
because this if statement

if (type != typeid(T))
return null;

...calls object.opEquals, which is not pure. So issue #13933 needs to be fixed
before we can solve this.

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[Issue 16662] Can't call std.variant.visit from a pure function

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

--- Comment #2 from Илья Ярошенко  ---
Variant's "get" method is not pure too. It was a big surprise. No I need to
figure out how to deal with it, the whole big project is pure.

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[Issue 16662] Can't call std.variant.visit from a pure function

[d-bugmail--- via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

Илья Ярошенко  changed:

   What|Removed |Added

 CC||ilyayaroshe...@gmail.com
   Severity|minor   |normal

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[Issue 16662] Can't call std.variant.visit from a pure function

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

--- Comment #1 from Paul Backus  ---
Seems like the culprit is VariantN.peek, which calls the property function
"type", which calls (through "fptr") an instance of the internal template
function "handler", which isn't pure.

Almost all of VariantN's operations use "handler" internally, so making it pure
would likely be difficult. On the other hand, modifying "fptr" to point to
different instances of "handler" is how VariantN keeps track of the type of the
stored object, so avoiding the use of "handler" would require substantial
changes to VariantN's implementation.

Here's the trail of breadcrumbs:

---

// test.d
import std.variant;

alias Example = Algebraic!(int, double);

void main() {
Example x;
pragma(msg, typeof(!int));
pragma(msg, typeof());
}

---

$ dmd test.d
inout(int)* delegate() inout @property @system
TypeInfo delegate() const nothrow @property @trusted

$ dmd --version
DMD64 D Compiler v2.074.0

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[Issue 16662] Can't call std.variant.visit from a pure function

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

Andrei Alexandrescu  changed:

   What|Removed |Added

 Status|NEW |ASSIGNED

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[Issue 16662] Can't call std.variant.visit from a pure function

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=16662

Andrei Alexandrescu  changed:

   What|Removed |Added

 CC||and...@erdani.com
   Assignee|nob...@puremagic.com|alexandru.razva...@gmail.co
   ||m

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