compound-assignment

Flags an assignment like x = x + n that can use a compound operator like x += n, or x++ and x--.

Why

In x = x + 1 the reader has to check that both sides really are the same x before they can read it as “increase x”. x++ says that directly.

What it flags

An assignment where the right side starts with the same target as the left, followed by an operator that has a compound form. The target can be a variable, a member like obj.x or an index like arr[i], and they can be nested.

What it leaves alone

• Targets where rewriting changes how often something runs, like arr[next()] = arr[next()] + 1.
• The target on the right of the operator, like x = 1 + x.
• Different targets on each side, like obj.x = obj.y + 1.

Example

// Before
x = x + 1;
x = x * n;
obj.count = obj.count + 3;
arr[i] = arr[i] * 2;

for (i = 0; i < 10; i = i + 1) {
    process(i);
}

// After
x++;
x *= n;
obj.count += 3;
arr[i] *= 2;

for (i = 0; i < 10; i++) {
    process(i);
}