Is it expected for this to not work as intended?
class Animal { }
class Person { }
type MyUnion = Number | Person;
var list: Array<MyUnion> = [ "aaa", 2, new Animal() ]; // Is this supposed to fail?
var x: MyUnion = "jjj"; // Should this actually pass?
Any suggestions on how to enforce strict type checking in this scenario?
When it comes to TypeScript, type compatibility is determined by structural subtyping.
Structural typing focuses on the members of types, rather than their names or declarations.
Specifically for classes:
Comparing two objects of a class type in TypeScript involves only comparing the members of the instance, without considering static members or constructors.
For further details, check out https://www.typescriptlang.org/docs/handbook/type-compatibility.html#classes
If there is any definition within Animal or Person, the following will not work:
class Animal { type: string; }
class Person { profession: string; }
type MyCombine = string | Person;
var collection: Array<MyCombine> = [ "apple", 3, new Animal() ]; // Currently leads to failure
var y: MyCombine = "orange"; // Currently leads to failure
In the absence of any declarations in Animal or Person, a string (or any other data) meets the criteria you are seeking.
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