In the D spec for pure functions it says that a pure function can override

"can override an impure function, but an impure function cannot override a pure one"

Can anyone help me how to do this ?

On Tuesday, 13 December 2016 at 04:48:11 UTC, Nikhil Jacob wrote:
> In the D spec for pure functions it says that a pure function can override
>
> "can override an impure function, but an impure function cannot override a pure one"
>
> Can anyone help me how to do this ?

what this means is

class Foo
{
   void foo() { ... }
}

class Bar : Foo
{
    override void foo() pure { ... }
}

is allowed. but

int someglobal;
class Foo
{
   void foo() pure { ... }
}

class Bar : Foo
{
    override void foo()  { someglobal = 42; }
}

in not.

On Tuesday, 13 December 2016 at 05:10:02 UTC, Nicholas Wilson wrote:
> On Tuesday, 13 December 2016 at 04:48:11 UTC, Nikhil Jacob wrote:
>> In the D spec for pure functions it says that a pure function can override
>>
>> "can override an impure function, but an impure function cannot override a pure one"
>>
>> Can anyone help me how to do this ?
>
> what this means is
>
> class Foo
> {
>    void foo() { ... }
> }
>
> class Bar : Foo
> {
>     override void foo() pure { ... }
> }
>
> is allowed. but
>
> int someglobal;
> class Foo
> {
>    void foo() pure { ... }
> }
>
> class Bar : Foo
> {
>     override void foo()  { someglobal = 42; }
> }
>
> in not.

I mistook the original statement to mean that an impure function can be called from a pure function with some manual overrides.

Thank you for the clarification.

On Tuesday, 13 December 2016 at 05:13:01 UTC, Nikhil Jacob wrote:
> I mistook the original statement to mean that an impure function can be called from a pure function with some manual overrides.
>
> Thank you for the clarification.

Yeah you can't do that, except in a debug statement. You can however cheat with SetFunctionAttributes (from std.traits).