strictPropertyInitialization don't works right with delegate initialization

[spat-ne-hochu]

TypeScript Version: 2.7.2

Code

class A {
    private b: number;
    private c: string;

    constructor(b: number) {
        this.b = b;
        this.initC();
        
    }

    private initC() {
        this.c = 'string';
    }
}

--strictNullChecks
--strictPropertyInitialization

Expected behavior:
no errors

Actual behavior:
Property 'c' has no initializer and is not definitely assigned in the constructor.

Playground Link:
https://goo.gl/uP2yKq

[Kingwl]

There are certain scenarios where properties can be initialized indirectly (perhaps by a helper method or dependency injection library), in which case you can use the new definite assignment assertion modifiers for your properties (discussed below).

https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-7.html

[spat-ne-hochu]

@Kingwl Definite
"Assignment Assertions" is a very bad practice, and I will not use it with serious projects, because it can very easily break the code.

it can check the constructor function.
why can not it test other methods for initialization?

[s-ve]

Duplicate of #21132 ?