use 5.010;

my %hash = (a => 1);

given(\%hash){           # first true
#given('a'){             # all true
    when('a' ~~ $_){
        say "explicit ~~";
        continue;
    }
    when($_ ~~ 'a'){
        say "reversed explicit ~~";
        continue;
    }
    when('a'){
        say "implicit ~~";
    }
}