Booleans

Start with the idea

A condition is not an arbitrary number or string in Rust. Comparisons such as builds > 0 and errors == 0 each produce a bool. The example combines them into ready, a name that expresses the decision the program needs to make. That makes the if branch easy to inspect: it runs only after at least one build exists and no errors remain. If your code says if count, rustc asks for a real boolean condition instead of guessing whether zero should mean false.

The logical operators also control which work is performed. For left && right, a false left side settles the answer, so right is not evaluated. For left || right, a true left side settles it. This is short-circuiting, shown in the diagram by the crossed-out right branch. It matters when the right expression is expensive or valid only after the left has checked a precondition. Do not use side effects on the right merely because you expect them to run: the operator may skip them.