Never type anything as mixed or any

How to do it

Replace it with the type, a union of the types, or unknown that must be narrowed before use. When data comes from outside, parse it into a type first.

Example

// Bad: any spreads, and nothing is checked
function total(order: any): any { return order.lines.reduce((sum: any, l: any) => sum + l.price, 0); }

// Good: named types end to end
type OrderLine = { readonly price: number; readonly quantity: number };
function total(lines: readonly OrderLine[]): number { return lines.reduce((sum, line) => sum + line.price * line.quantity, 0); }

# Bad
def total(order: Any) -> Any: ...

# Good
@dataclass(frozen=True)
class OrderLine:
    price: int
    quantity: int

def total(lines: list[OrderLine]) -> int:
    return sum(line.price * line.quantity for line in lines)

// Bad: mixed turns off the checks
function total(mixed $order): mixed { /* ... */ }

// Good: a list of typed lines
/** @param list<OrderLine> $lines */
function total(array $lines): int { return array_sum(array_map(fn (OrderLine $line) => $line->price * $line->quantity, $lines)); }

How to check

The build fails on it. Examples are TypeScript noImplicitAny with @typescript-eslint/no-explicit-any, PHPStan level 10, which checks explicit and implicit mixed, and mypy --disallow-any-explicit.