Type recast

[kratess]

🔎 Search Terms

"recast", "type recast", "2322"

🕗 Version & Regression Information

Version 5.5.4

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/JYOwLgpgTgZghgYwgAgILIN4Chm+QVwGdoQ4BbCALkxzzqJPKuULClAHMBuW3AX2QAfZCHwAbMTz5YsoSLEQoAQjXrEopCtWx01jLSzacedadKwx8IBGGAB7EMkisAFAEpVeBA9bI41dABeT10CdU1mHVDdBg0magAiZzAE3l1pUxk6YBhkFzgAOliI5ECykXExDygIMHwNHjSxWuQAI2oVYLgTLx87ZoKxOw4XVrcsaWT3LiA

💻 Code

interface A {
    username: {
        username: string;
    } | null;
}

interface B {
    username: {
        username: string;
    }
}

function test() {
    const a: A = {
        username: {
            username: "test"
        }
    }

    if (a.username === null) return;

    let b: B = a;
    console.log(b)
}
test();

🙁 Actual behavior

Type 'A' is not assignable to type 'B'.
Types of property 'username' are incompatible.
Type '{ username: string; } | null' is not assignable to type '{ username: string; }'.
Type 'null' is not assignable to type '{ username: string; }'.

🙂 Expected behavior

I know why this error message is shown up but I wonder, wouldn't it be better that the type should be recasted after the if statement? Down the lines username object cannot be null. indeed the function stops if the object is null

Additional information about the issue

No response

[nmain]

Duplicate of #42384. Search terms: "parent narrowing".

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.