Looks like its a typo :(<p>The correct way to go about this would be to return the new balance and capture the return value in the first part of the out postcondition like:<p>```D
double deposit(double amount)
in (amount > 0, "Deposit amount must be positive")
out (result; result == balance)
{
balance += amount;
return balance;
}
```<p>My mistake!<p><a href="https://dlang.org/spec/function.html#postconditions" rel="nofollow">https://dlang.org/spec/function.html#postconditions</a>
I've never used D, but it appears to be valid syntax. <a href="https://dlang.org/spec/function.html#postconditions" rel="nofollow">https://dlang.org/spec/function.html#postconditions</a>