string & Type intersection produce error in switch statement

[mdaveynis]

TypeScript Version: 2.0.2

Code

class MyBrand
{
 private _a;
}

function test(strInput: string & MyBrand, numInput: number & MyBrand) {
 switch(strInput)
 {
 case "a": // error: Type '"a"' is not comparable to type 'string & MyBrand'
 return 1;
 }

 switch(numInput)
 {
 case 1: // error: Type '1' is not comparable to type 'number & MyBrand'
 return 1;
 }

 return 0;
}

Expected behavior:
No error reported in case statements.

Actual behavior:
See above error report inline.

[nippur72]

Why do you expect no error? Member _a is private but it must be present. In other words MyBrand is not an alias for {} just because _a is private.

[iskiselev]

Before 2.0.2 it was a way to create branded strings or numbers.
So, it was possible to create method, that will accept only some strings. For example, I was able to mark introduce type ProductId = string & ProductBrand. After it, objects that was returned by method with ProductId return type was accepted by any method that accept string, but it was possible to create method that accept only ProductId string.
With 2.0.2 this functionality is partially broken.

[falsandtru]

also

type Id = {id:never} & number;
<Id>1 > <number>0;
<Id>1 > 0;

$ node built/local/tsc.js -t es5 -m commonjs --lib es6 --strictNullChecks index.ts && node index.js
index.ts(3,1): error TS2365: Operator '>' cannot be applied to types 'Id' and '0'.

[sandersn]

Note that this works with if:

 if (strInput === 'a') {
 return 1;
 }
 if (numInput === 1) {
 return 1;
 }

Does not give any errors. switch should work the same as if with ===.