Specialized function overloading (type guards)

[olegdunkan]

Sorry, It maybe duplicate, but I can't find an issue.
Let we have this code:

class C {
    x:number;
}
function fn(name:"a" );
function fn(name:"b", x:string );
function fn(name:"c", x:C);
function fn(name:"a"|"b"|"c", x?:string|C) {
    if (name ==="c") {
        x.x = 1; //error     
    }
}

We can infer that x has C type inside "c" = true branch of the condition.
Is there special type guard for this case?
If isn't then are there any plans to support this behavior?

[RyanCavanaugh]

#14515

[olegdunkan]

@RyanCavanaugh thanks