C++17 allows scoped enums to be initialized with integers as long as it's not narrowing, e.g. #include <cstdint> enum class e16 : uint16_t { x16, y16 }; enum class e32 : uint32_t { x32, y32 }...

Why does TypeScript not apply type narrowing on members of objects to the object type itself, such that it can be passed to another function that expects a narrowed type? How can this be fixed/circ...

Consider I have a python class that has a attributes (i.e. a dataclass, pydantic, attrs, django model, ...) that consist of a union, i.e. None and and a state. Now I have a complex checking functio...

Consider this simple snippet. I'm also pasting it here: type A = | { b: number; } | { c: number; }; function f1(a: A) { if ('b' in a) { return a['b']; // No problem! } return 42; } func...

Typescript refuses to narrow with a call to fail but will narrow with a call to fail2. Is this a bug in typescript? const fail = (message?: string): never => { throw new Error(message); }; fun...

Why do tests 1 and 2 work here, but test 3 shows a compiler error at foo[barConst]++: 'Object is possibly "undefined".'? I often need to access properties via bracket notation and thus li...

In typescript: let str: string = 'abc'; let val: unknown = 'test'; if (typeof val === 'string') { str = val; } // this code does not report any error, everything works fine. but, if I change th...

I would like to link 2 generics types in a function, and use narrowing for both types by checking one of them. What is the correct way to do this? type A = 'A'; type B = 'B'; type AB = A | B type...

Why do I get a Cannot invoke an object which is possibly 'undefined' Typescript error even after I check that the func reference is not undefined? type Hoge = { func?: (str: string) => boolean ...

Note: TypeScript is invoked with tsc --strict for all code shown below. Given a singleton object o: const o = { foo: 1, bar: 2, baz: 3, }; If I have a string value (say from user input) that ca...

VS Code Version: I'm trying some 'Type Narrowing' Code in VS Code, but VS Code gives a different type of information than TypeScript Playground: VS Code gives: the return type of Document.getEleme...

function isFish(pet: Fish | Bird): pet is Fish { return (<Fish>pet).swim !== undefined; } tells typescript that pet type is Fish Is there a way to state the contrary, that the input param...

I have a problem when I try to use instanceof with derived class instances in a if-else statement. Consider the following example: interface IBaseModel { id: string } class BaseClass { model: I...

I read about narrowing conversion on the cpp reference website. I kind of understood it but what i am not getting is that why is the error present only in the first line. long double ld = 3.14159...

The following line of code is accepted by the compiler (sun-jdk-8u51) without any warnings or errors: short b = true ? 1 : 1; Whereas the next two code lines lead to a compilation error (incompa...