typescript discriminated union type

Discriminated union - what this means is you get to say i want certain properties if my type is defined in a certain way.

// discriminated union

interface IPizza {

foodtype : 'pizza'

crust : string

}

interface ISandwich {

foodtype : 'sandwich'

bread : string

}

type Food = IPizza | ISandwich

const myfood : Food = {

foodtype : 'pizza',

crust : 'thin'

}

const sandwich : Food = {

foodtype : 'sandwich',

bread : 'wholemeal'

}

If i tried to define foodtype that is of 'pizza' to contain 'bread' property, i will get an error

const myfood : Food = {

foodtype : 'pizza',

bread : 'thin' // error

}