+= doesn't count a private member as being used

[qian357891]

🙁 Actual behavior

TS didn't recognize +=，if I use private in the constructor
tsc version：4.8.4

💻 Code

demo.ts

class Account {
  nickname?: string;
  constructor(
    public readonly id: number,
    public name: string,
    private _balance: number //error TS6138: Property '_balance' is declared but its value is never read.
  ) {}
  deposit(amount: number): void {
    this._balance += amount;
    // this._balance = this._balance + amount;
  }
}

And I split += it is useful.

class Account {
  nickname?: string;
  constructor(
    public readonly id: number,
    public name: string,
    private _balance: number //pass
  ) {}
  deposit(amount: number): void {
    // this._balance += amount;
    this._balance = this._balance + amount;
  }
}

tsconfig.json

{
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  }
}

[MartinJohns]

Using the addition assignment operator does not count as reading a property. This is working as intended. Once you actually use _balance somewhere the error will disappear.

There's a duplicate somewhere, didn't find it so far. edit: Found it. #42422 (comment)

[qian357891]

使用加法赋值运算符不算作读取属性。这正在按预期工作。一旦你实际在某个地方使用，错误就会消失。_balance

某处有重复项，到目前为止没有找到。编辑：找到了。#42422（评论）

@MartinJohns
Could you please tell me the principle? This seems a bit counterintuitive.

[MartinJohns]

I don't know what you mean by that question. When you read a variable, it's used. Just assigning something to it using += does not qualify as being read.

[DanielRosenwasser]

The only thing "reading" from the variable _balance is _balance itself. If something else read from _balance, then that would count as being used.

[typescript-bot]

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