Access ReactiveVar // Template.instance() from helper (indirectly)

Question

How can I access ReactiveVar in the construction like below?

Template.profile.helpers({
    user: {
        ...
        gender: () => Template.instance().genderFlag.get(), //returns Uncaught TypeError: Cannot read property 'genderFlag' of null
        ...
    },
});

Returns error because Template.instance() inside gender: is null (when I console.log(Template.instance());)

This is how I create ReactiveVar:

Template.profile.onCreated( function() {
  this.genderFlag = new ReactiveVar(0);
});

P.S. gender is inside user because I use user context i.e. {{#with user}} in my .html.

UPDATE:

Spacebars part:

<button type="button" name="Male" class="{{#if gender '1'}}gender--selected{{/if}}">Male</button>
<button type="button" name="Female" class="{{#if gender '2'}}gender--selected{{/if}}">Female</button>

so I am passing arg to the Template.helper gender:

user: {
   ...
   gender: (arg) => arg == Template.instance().genderFlag.get(),
   ...
}

Answer 1

Because you are creating a function within the helper it seems to be picking up the wrong data context and therefore the Template variable is not available a the time it is called, the following code works, it moves the function to the helper itself so the context is correct and it can access Template.instance() correctly, then you can return an object for user as needed for your #with

Template.profile.helpers({
  user: () => { 
    return { 
        ...
        gender: Template.instance().genderFlag.get() 
        ...
    };
  }
});

EDIT:

In line with the update to your question, couple of options but neatest I would say is:

Template.profile.helpers({
  user: () => { 
    var gend = Template.instance().genderFlag.get();
    return { 
        ...
        gender: gend,
        isMale: gend===1?"gender--selected":"",
        isFemale: gend===2?"gender--selected":"",
        ...
    };
  }
});

And in your handlebars

<button type="button" name="Male" class="{{isMale}}">Male</button> 
<button type="button" name="Female" class="{{isFemale}}">Female</button>