Hi,

I have a class `Image`, and I have a function called `getSubImage(Rect bounds)`. What I can't figure out is how to get the result of `getSubImage()` to take on the constness of the backing image.

ie.
    //The Image class is really just a view over a buffer that's managed elsewhere
    const(Image).getSubImage(...) -> const(Image)

    Image.getSubImage(...) -> Image

I tried to do this with `inout`, but that requires that a parameter in the function be `inout`. I don't suppose I could somehow declare `this` to be inout?

Thanks

On Sunday, 17 September 2017 at 21:18:08 UTC, David  Zhang wrote:
> Hi,
>
> I have a class `Image`, and I have a function called `getSubImage(Rect bounds)`. What I can't figure out is how to get the result of `getSubImage()` to take on the constness of the backing image.
>
> ie.
>     //The Image class is really just a view over a buffer that's managed elsewhere
>     const(Image).getSubImage(...) -> const(Image)
>
>     Image.getSubImage(...) -> Image
>
> I tried to do this with `inout`, but that requires that a parameter in the function be `inout`. I don't suppose I could somehow declare `this` to be inout?
>
> Thanks

I am aware that you can duplicate the method, but it seems a bit unwieldy and excessive.

Nevermind! I rediscovered the `inout`attribute.

Though if I may say so, I have no idea how `inout` is supposed to indicate "whatever the constness of a".

On 9/17/17 5:37 PM, David Zhang wrote:
> Nevermind! I rediscovered the `inout`attribute.

Correct, inout applied to the function is actually applying to the 'this' parameter. Same as const or immutable functions as well.

> 
> Though if I may say so, I have no idea how `inout` is supposed to indicate "whatever the constness of a".
> 

What inout does is look at the mutability of the parameter and transfer it to the mutability of the return type.

-Steve