help | how to use(or possibility to) mixin with function?

in my case
first I use function to create a .in-10 ...

@selectors: 5, 10, 20;
each(@selectors, {
    .in-@{value}{
        padding: (@value)px;
    }
});

then use .in-10 as a mixin to .button

.button{
    .background-color:  green;
    .in-10();  /* <--  here to use mixin */
    ...some other
}

an error say .in-10 is undefined, may I think they are output same time so that .in-10 is not find, how can I make this work? how to code less in this case?

I can't got any answer in stackoverflow so I try here, pls help!

The issue provides only Less snippets and names no repository files, tests, or entry points. Start by reproducing the undefined-mixin error with the shown selector loop, then review the project's documented semantics for generated mixins; done would require a confirmed explanation or documentation of the supported approach.